Shale gas permeability calculation model construction method based on PD-FDM coupling

Abstract

The invention belongs to the field of shale gas permeability calculation, particularly relates to a shale gas permeability calculation model construction method based on PD-FDM coupling, and aims to solve the problems of low efficiency and accuracy of shale gas permeability calculation in the prior art. The method comprises the steps that near-field dynamics and a finite difference method are coupled, and a shale gas reservoir fluid-solid coupling model is constructed; setting definite solution conditions according to actual crustal stress conditions and reservoir environment of the shale gas reservoir; after the initial crustal stress is balanced according to the definite solution condition, analyzing the influence of a fluid layer on a solid layer and the influence of the solid layer on the fluid layer in combination with a shale gas reservoir fluid-solid coupling model; and calculating the shale gas permeability by combining the influence of the fluid layer on the solid layer and the influence of the solid layer on the fluid layer. The near-field dynamics, the finite element method and the finite difference method are coupled, and the permeability of the shale gas can be quickly and accurately simulated and calculated.

Description

Background Art

[0002] As a potential unconventional resource, shale gas has broad development prospects. However, the seepage mechanism of shale gas is complex, and the micro-nano pore / fracture structure is intricate. Rapidly and effectively evaluating the permeability of shale gas has always been the focus of scholars and engineers at home and abroad.

[0003] To obtain the seepage situation of shale gas, various numerical simulation calculation methods have been proposed currently: the finite element method (FEM) based on traditional continuum mechanics. The finite element method assumes that there is a continuously differentiable displacement field near any point in the structure. However, there are many discontinuities in shale fractures, and it is difficult to obtain the partial differential equation of the displacement field in the discontinuous region.

[0004] Peridynamics (PD) is a numerical method that establishes a model based on the idea of non-local action and describes mechanical behavior through integral equations. It has unique advantages in simulating continuous-discontinuous problems, and can also simulate fluid seepage, enabling fluid-structure interaction simulation within a unified framework. However, due to its non-local action, the computational cost is much larger than that of the classical continuum theory. When calculating large-scale problems, it occupies too much computing resources. In fluid-structure interaction calculations, the fluid is solved explicitly, and the required computing resources for iteration are more, resulting in different convergence speeds of the fluid and the solid, and it is difficult to balance efficiency and effect.

[0005] The finite difference method (FDM) is an approximate method for solving the numerical solution of differential equations. Its main principle is to directly approximate the differential terms in the differential equation, thereby transforming the differential equation into a system of algebraic equations for solution. The principle of the finite difference method is simple, and it is a numerical calculation method with a wide adaptability, strong problem-solving ability, and good generality.

[0006] Therefore, the present invention proposes a method for constructing a shale gas permeability calculation model based on PD-FDM coupling, which utilizes the advantages of various methods and applies them to the establishment / calculation of corresponding units to rapidly and accurately simulate and calculate the permeability of shale gas. Summary of the Invention

[0007] To solve the above problems in the prior art, that is, the problems of low efficiency and accuracy in calculating the permeability of shale gas in the prior art, in the first aspect of the present invention, there is provided a method for constructing a shale gas permeability calculation model based on PD-FDM coupling for calculating the permeability of shale gas, including:

[0008] Step S10, coupling peridynamics and the finite difference method to construct a fluid-structure interaction model for a shale gas reservoir; the fluid-structure interaction model for the shale gas reservoir includes a solid layer, a fluid layer, and a transition layer;

[0009] Step S20, set the definite solution conditions according to the actual in-situ stress conditions and reservoir environment of the shale gas reservoir; when the initial in-situ stress is balanced according to the definite solution conditions, combine the fluid-solid coupling model of the shale gas reservoir to analyze the influence of the fluid layer on the solid layer and the influence of the solid layer on the fluid layer;

[0010] Step S30, calculate the shale gas permeability by combining the influence of the fluid layer on the solid layer and the influence of the solid layer on the fluid layer.

[0011] In some preferred embodiments, the fluid-solid coupling model of the shale gas reservoir is constructed by coupling peridynamics and the finite difference method, and the method is as follows:

[0012] Establish the solid layer: establish the solid skeleton in the central area of the fractured shale based on peridynamics, and model the shale reservoir at the boundary based on the finite element method;

[0013] Establish the fluid layer: establish a fluid layer that depicts the action of the fluid in the pores of the shale based on the finite difference method;

[0014] Establish the transition layer: the transition layer is arranged between the fixed layer and the fluid layer, and the transition layer inserts into the coupling interface of the fluid layer-solid layer to perform parameter interaction.

[0015] In some preferred embodiments, the method for analyzing the influence of the fluid layer on the solid layer is as follows:

[0016] Shale is a porous medium, and the change in the fluid pressure in its pores will cause the deformation of the shale matrix and the redistribution of stress; in the possible fracture generation area described by peridynamics, the fluid layer grids and the material points of the solid layer with the same scale correspond to each other. Through the transition layer, the shale pore pressure and saturation are calculated by combining the seepage model, and the shale pore pressure and the saturation are transmitted to the corresponding material points to correct the deformation parameters of the solid layer;

[0017] In the far-field area described by the finite element method as the boundary weakens the influence of the boundary conditions, larger finite elements correspond to multiple fluid layer grids, the grid centers correspond to the finite element nodes, and the seepage parameter value of each finite element is the average value of the seepage parameters of the corresponding number of grid nodes.

[0018] In some preferred embodiments, the method for analyzing the influence of the solid layer on the fluid layer is as follows:

[0019] In the possible fracture generation area described by peridynamics, the fluid layer grids and the material points of the solid layer with the same scale correspond to each other. Through the transition layer, the volumetric strain obtained by the material points from the stress field is used to correct the porosity and permeability values of the corresponding fluid layer grids;

[0020] In the far - field region described by the finite - element method, which weakens the influence of boundary conditions as a boundary, the finite - element transfers to the fluid - layer grid, and at this time, the transition layer is controlled by the finite - difference grid.

[0021] In some preferred embodiments, based on the influence of the fluid layer on the solid layer and the influence of the solid layer on the fluid layer, the shale - gas permeability is calculated. The method is as follows:

[0022] Combining the peridynamic damage field, the region in the fluid - solid coupling model of the shale - gas reservoir is divided into a solid domain, a transition domain, and a fracture domain;

[0023] According to the influence of the fluid layer on the solid layer and the influence of the solid layer on the fluid layer, calculate the shale - gas permeability corresponding to the solid domain, the transition domain, and the fracture domain;

[0024] The calculation method of the shale - gas permeability in the solid domain is as follows: When only elastic deformation occurs in the solid domain and no damage or fracture is generated, the permeability of the fluid grid nodes corresponding to the finite - element region does not change. Therefore, the permeability of the rock matrix is the shale - gas permeability of the solid domain;

[0025] The calculation method of the shale - gas permeability in the transition domain is as follows: Construct a linear function according to the division index corresponding to the transition domain; Based on the linear function, obtain the shale - gas permeability of the transition domain from the difference in permeability between the solid domain and the fracture domain;

[0026] The calculation method of the shale - gas permeability in the fracture domain is as follows: Based on the fracture aperture, obtain the shale - gas permeability of the fracture domain through the cubic law.

[0027] In some preferred embodiments, combining the peridynamic damage field, the region in the fluid - solid coupling model of the shale - gas reservoir is divided into a solid domain, a transition domain, and a fracture domain. The method is as follows:

[0028]

[0029] where χ r and χ f are set division indexes, represents the peridynamic damage - field characterization quantity.

[0030] In the second aspect of the present invention, a system for constructing a shale - gas permeability calculation model based on PD - FDM coupling is proposed for calculating shale - gas permeability. The system includes:

[0031] A model - construction module, configured to couple peridynamics and the finite - difference method to construct a fluid - solid coupling model of the shale - gas reservoir; The fluid - solid coupling model of the shale - gas reservoir includes a solid layer, a fluid layer, and a transition layer;

[0032] An impact analysis module, configured to set definite solution conditions according to the actual in-situ stress conditions and reservoir environment of the shale gas reservoir; when, according to the definite solution conditions, after the initial in-situ stress is balanced, in combination with the fluid-solid coupling model of the shale gas reservoir, analyze the impact of the fluid layer on the solid layer and the impact of the solid layer on the fluid layer;

[0033] A permeability calculation module, configured to calculate the shale gas permeability in combination with the impact of the fluid layer on the solid layer and the impact of the solid layer on the fluid layer.

[0034] In a third aspect of the present invention, an electronic device is proposed, including:

[0035] At least one processor; and a memory communicatively connected to at least one of the processors; wherein, the memory stores instructions executable by the processor, and the instructions are used to be executed by the processor to implement the above-mentioned method for constructing a shale gas permeability calculation model based on PD-FDM coupling.

[0036] In a fourth aspect of the present invention, a computer-readable storage medium is proposed, and the computer-readable storage medium stores computer instructions, and the computer instructions are used to be executed by the computer to implement the above-mentioned method for constructing a shale gas permeability calculation model based on PD-FDM coupling.

[0037] Advantages of the present invention:

[0038] 1) The present invention couples peridynamics (PD) and the finite difference method (FDM), uses the ordinary state peridynamics and finite element hybrid modeling to describe the deformation and fracture of solids, and on this basis, uses the finite difference method to control the fluid seepage problem based on Darcy's law, thereby comprehensively improving the fluid-solid coupling calculation efficiency from both the solid and fluid aspects, and can quickly and accurately simulate and calculate the permeability of shale gas.

[0039] 2) The method for constructing a shale gas permeability calculation model based on PD-FDM fluid-solid coupling provided by the present invention has a wide adaptability, strong problem-solving ability, good generality for calculating fluid flow problems, high efficiency and good accuracy in simulating and calculating the permeability. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, objects and advantages of the present application will become more apparent:

[0041] Figure 1 is a schematic flowchart of a method for constructing a shale gas permeability calculation model based on PD-FDM coupling according to an embodiment of the present invention;

[0042] Figure 2 It is a schematic diagram of the framework process of a system for constructing a shale gas permeability calculation model based on PD-FDM coupling according to an embodiment of the present invention;

[0043] Figure 3 It is a schematic diagram of the action of a fluid layer on a solid layer according to an embodiment of the present invention;

[0044] Figure 4 It is a schematic diagram of the action of a solid layer on a fluid layer according to an embodiment of the present invention;

[0045] Figure 5 It is a schematic diagram of the division of a solid domain, a transition domain and a fracture domain according to an embodiment of the present invention. Specific embodiments

[0046] The following further elaborates on the present application in conjunction with the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related invention and do not limit the invention. Additionally, it should be noted that for the sake of convenience of description, only parts related to the relevant invention are shown in the drawings.

[0047] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The following will elaborate on the present application in detail with reference to the drawings and embodiments.

[0048] A method for constructing a shale gas permeability calculation model based on PD-FDM coupling according to the first embodiment of the present invention is used to calculate the shale gas permeability. As Figure 1 shown, it includes:

[0049] Step S10: Couple peridynamics and the finite difference method to construct a fluid-solid coupling model for a shale gas reservoir; the fluid-solid coupling model for the shale gas reservoir includes a solid layer, a fluid layer, and a transition layer;

[0050] Step S20: Set the definite solution conditions according to the actual in-situ stress conditions and reservoir environment of the shale gas reservoir; when the initial in-situ stress is balanced according to the definite solution conditions, in combination with the fluid-solid coupling model for the shale gas reservoir, analyze the influence of the fluid layer on the solid layer and the influence of the solid layer on the fluid layer;

[0051] Step S30: Calculate the shale gas permeability in combination with the influence of the fluid layer on the solid layer and the influence of the solid layer on the fluid layer.

[0052] To more clearly illustrate the method for constructing a shale gas permeability calculation model based on PD-FDM coupling of the present invention, the following elaborates on each step in the method embodiment of the present invention in conjunction with the drawings.

[0053] The present invention is directed to a shale gas reservoir, which couples peridynamics (PD) and the finite difference method (FDM) to establish a fluid layer, a solid layer, and a coupling layer (i.e., a transition layer) that connects the two and performs data iteration. In the solid layer, PD and FEM are used to discretize the region where fractures may form in the near field into a series of material points that can characterize mass and physical properties, and the region with the far field as the boundary is discretized into a series of finite elements composed of nodes (i.e., the near-field dynamics modeling is used for the region where the solid may rupture, and the finite element modeling is used for the elastic deformation part in the far field); in the fluid layer, the FDM is used to form a finite fluid grid; through the coupling layer, parameter interaction between the fluid layer and the solid layer is carried out, and the stress field and seepage field are iteratively corrected;

[0054] Before calculating the shale gas permeability, the definite solution conditions including initial conditions and boundary conditions are applied as boundaries to the model for constraint; before fluid-solid coupling, in view of the shale gas reservoir, in-situ stress balance is carried out, initial parameter calculation is performed based on the definite solution conditions, and then parameter mutual iteration correction between the seepage field and the stress field is carried out; based on the peridynamic bond theory, with the critical bond elongation rate that can match the fracture energy as an index, it is judged whether fractures occur; the displacement and strain obtained after the solid layer is loaded are transferred to the fluid layer, and the pressure in the fluid layer is solved, so as to quickly and accurately simulate the change of shale gas permeability. Specifically as follows:

[0055] Step S10, couple peridynamics and the finite difference method to construct a fluid-solid coupling model for a shale gas reservoir; the fluid-solid coupling model for the shale gas reservoir includes a solid layer, a fluid layer, and a transition layer;

[0056] In this embodiment, the process of constructing the fluid-solid coupling model for the shale gas reservoir is as follows:

[0057] Establish a solid layer: According to the actual project, establish a solid model of a shale gas reservoir with a certain scale. This part of the model is used to simulate the solid skeleton particles. Respectively, based on peridynamics, establish the solid skeleton of the central region of the fractured shale (i.e., the region where fractures may form, selected according to the actual situation), and based on the finite element method, model the shale reservoir with the farther part as the boundary (i.e., the boundary region);

[0058] Establish a fluid layer: Shale is a porous medium with fluid inside. Based on the finite difference method, establish a fluid layer that can depict the action of the fluid in the pores;

[0059] Establish a transition layer: In the fluid-solid coupling process, design the database exchange between the solid layer and the fluid layer, and establish a coupling interface between the fluid-solid layers as the parameter interaction center; the coupling interface serves as a control interface. When the fluid pressure is transmitted to the solid layer, it is controlled by material points and finite elements. At this time, the interface can accurately determine the corresponding grid of the material point receiving the fluid pressure through the position information of the material points, finite elements, and fluid grids; when the solid deformation is transmitted to the fluid, the transition layer is controlled by the fluid grid, and based on the position information and the permeability coefficient of the material points and finite elements, the deformation is transmitted to the fluid grid.

[0060] The fluid layer based on the finite difference method and the solid layer based on peridynamics are discretized into grids and material points with smaller sizes, and the far-field region based on the finite element method is discretized into finite elements with larger sizes. The relative positions of the three are determined through their coordinates.

[0061] Step S20: Set the definite solution conditions according to the actual in-situ stress conditions and reservoir environment of the shale gas reservoir; when the initial in-situ stress is balanced according to the definite solution conditions, combined with the fluid-solid coupling model of the shale gas reservoir, analyze the influence of the fluid layer on the solid layer and the influence of the solid layer on the fluid layer.

[0062] In this embodiment, first set the definite solution conditions according to the actual in-situ stress conditions and reservoir environment of the shale gas reservoir. The definite solution conditions include setting surface forces and surface displacements on the shale skeleton, setting initial pore pressure and initial saturation for the initial conditions, and setting pore pressure boundary pore pressure and pressure drop gradient for the boundary conditions; according to the definite solution conditions, before the fluid-solid coupling iteration, through the equilibrium relationship between the displacement and external load of the shale gas reservoir rock in the initial equilibrium state before exploitation, calculate the initial in-situ stress of each point in the shale gas reservoir for in-situ stress balance. After the initial in-situ stress balance, start to analyze the influence of the fluid layer on the solid layer and the influence of the solid layer on the fluid layer. Specifically as follows:

[0063] Analyze the influence of the fluid layer on the solid layer, as Figure 3 shown, the method is:

[0064] Shale is a porous medium, and the change in the fluid pressure in its pores will cause the deformation and stress redistribution of the shale matrix; in the possible fracture generation area described by peridynamics, the fluid layer grids and the material points of the solid layer with the same scale correspond to each other. Through the coupling layer, the shale pore pressure and its saturation obtained by calculating through the seepage model will be transmitted to the corresponding material points to correct the deformation parameters of the solid layer (specifically: the change in pore pressure and saturation will cause the loading and unloading of the shale gas reservoir. Take the increment of the shale self-weight caused by this change as a new load, and then obtain the change in displacement, strain, and stress caused by the load increment).

[0065] In the far-field region described by the finite element method, which weakens the influence of boundary conditions as the boundary, larger finite elements correspond to multiple meshes, the center of the mesh corresponds to the nodes of the finite element, and the seepage parameter value of each finite element is the average of the seepage parameters of the corresponding number of mesh nodes.

[0066] The flow field in the saturated porous fractured medium is described by Darcy's law:

[0067]

[0068] where μ is the viscosity of the injected fluid, K is the permeability tensor of the shale, and P is the fluid pressure.

[0069]

[0070] In the formula, P e is the fluid pressure within the finite element of the solid part, and P i is the water pressure at the mesh node of the fluid part. l is the element width, h is the element thickness, n is the number of fluid meshes contained within the finite element, and i = 1, 2, 3... n.

[0071] Moreover, according to the positions of the nodes within the element, the signs of the water loads in the x and y directions at each node can be determined. That is, the signs of the fluid loads in the x and y directions at the node are successively negative-negative, negative-positive, positive-positive, and positive-negative; for the element nodes shared by multiple elements, the fluid loads thereon are obtained by superposition.

[0072] Analyze the influence of the solid layer on the fluid layer, as Figure 4 shown, and the method is as follows:

[0073] In the region where cracks may be generated described by peridynamics, the fluid layer meshes and the material points of the solid layer with the same scale correspond to each other. Through the coupling layer, the volumetric strain obtained by the material points from the stress field is used to correct the porosity and permeability values of the corresponding meshes (specifically: the permeability and porosity of the shale gas reservoir are related to the deformation of the shale gas reservoir skeleton. The grid physical property parameters can be updated iteratively by the function of pore pressure and effective stress combined with the deformation type auxiliary equation with the change value of volumetric strain);

[0074] In the far-field region described by the finite element method, which weakens the influence of boundary conditions as the boundary, this correction process is transferred from the finite element to the mesh, and at this time, the transition layer is controlled by the finite difference mesh.

[0075] Step S30, combining the influence of the fluid layer on the solid layer and the influence of the solid layer on the fluid layer, calculate the shale gas permeability.

[0076] In this embodiment, the regions in the model are divided into a solid domain, a transition domain, and a fracture domain: the three regions are distinguished according to the peridynamic damage field, and dividing the regions is beneficial to interpolating the solid permeability of the transition domain as Figure 5 shown as follows:

[0077]

[0078] where χ r and χ f are set division indicators, represents the peridynamic damage field characterization quantity.

[0079] Calculate the shale gas permeabilities corresponding to the solid domain, the transition domain, and the fracture domain according to the influence of the fluid layer on the solid layer and the influence of the solid layer on the fluid layer;

[0080] The calculation method for the shale gas permeability of the solid domain is as follows: when only elastic deformation occurs in the solid domain and no damage or fracture occurs, the permeability of the fluid grid nodes corresponding to the finite element region does not change. Therefore, the permeability of the rock matrix is the shale gas permeability of the solid domain;

[0081] The calculation method for the shale gas permeability of the transition domain is: construct a linear function according to the division indicator corresponding to the transition domain; that is a represents the corresponding value of the linear indicator, and c1, c2 are fixed values of the linear indicator, which are 0.2 and 0.4 respectively.

[0082] Based on the linear function, obtain the shale gas permeability of the transition domain from the permeability difference between the solid domain and the fracture domain:

[0083] k = χ r k r + χ f k f (4)

[0084] where k represents the solid permeability of the transition domain, k r represents the permeability of the solid domain, and k f represents the permeability of the fracture domain.

[0085] The calculation method for the shale gas permeability of the fracture domain is: based on the fracture aperture, obtain the shale gas permeability k f of the fracture domain through the cubic law:

[0086]

[0087] where b represents the fracture aperture.

[0088] The system for constructing a shale gas permeability calculation model based on PD-FDM coupling according to the second embodiment of the present invention is used to calculate the shale gas permeability, as Figure 2 shown. The system includes:

[0089] A model construction module 100, configured to couple peridynamics and the finite difference method to construct a fluid-solid coupling model of a shale gas reservoir; the fluid-solid coupling model of the shale gas reservoir includes a solid layer, a fluid layer, and a transition layer;

[0090] An influence analysis module 200, configured to set definite solution conditions according to the actual in-situ stress conditions and reservoir environment of the shale gas reservoir; when, according to the definite solution conditions, the initial in-situ stress is balanced, combining with the fluid-solid coupling model of the shale gas reservoir, analyze the influence of the fluid layer on the solid layer and the influence of the solid layer on the fluid layer;

[0091] A permeability calculation module 300, configured to calculate the shale gas permeability by combining the influence of the fluid layer on the solid layer and the influence of the solid layer on the fluid layer.

[0092] Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working process and related explanations of the above-described system can refer to the corresponding process in the foregoing method embodiment, and will not be repeated here.

[0093] It should be noted that the system for constructing a shale gas permeability calculation model based on PD-FDM coupling provided in the above embodiment is only illustrated by dividing the above functional modules. In actual applications, the above functions can be allocated to different functional modules according to needs, that is, the modules or steps in the embodiments of the present invention can be further decomposed or combined. For example, the modules in the above embodiment can be combined into one module, or further split into multiple sub-modules to complete all or part of the functions described above. The names of the modules and steps involved in the embodiments of the present invention are only for distinguishing each module or step, and are not regarded as an improper limitation of the present invention.

[0094] A device for constructing a shale gas permeability calculation model based on PD-FDM coupling according to the third embodiment of the present invention includes at least one processor; and a memory communicatively connected to at least one of the processors; wherein, the memory stores instructions executable by the processor, and the instructions are used to be executed by the processor to implement the above method for constructing a shale gas permeability calculation model based on PD-FDM coupling.

[0095] A computer-readable storage medium according to a fourth embodiment of the present invention, wherein the computer-readable storage medium stores computer instructions for being executed by a computer to implement the above-mentioned method for constructing a shale gas permeability calculation model based on PD-FDM coupling.

[0096] Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes and related descriptions of the above-described shale gas permeability calculation model construction device and computer-readable storage medium based on PD-FDM coupling can refer to the corresponding processes in the foregoing method embodiments and will not be elaborated herein.

[0097] Those skilled in the art should be able to realize that the modules and method steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of the two. The programs corresponding to the software modules and method steps can be placed in a random access memory (RAM), internal memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art. To clearly illustrate the interchangeability of electronic hardware and software, the components and steps of each example have been generally described according to functions in the above description. Whether these functions are executed in the form of electronic hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0098] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, so that a process, method, article, or device / equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent in these processes, methods, articles, or devices / equipment.

[0099] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the drawings. However, those skilled in the art can easily understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the protection scope of the present invention.

Claims

1. A method for constructing a shale gas permeability calculation model based on PD-FDM coupling, which is used to calculate the shale gas permeability, is characterized in that, The method includes the following steps: Step S10: Couple peridynamics and the finite difference method to construct a fluid-solid coupling model for shale gas reservoirs. The fluid-solid coupling model for shale gas reservoirs includes a solid layer, a fluid layer, and a transition layer; Step S20: Set the definite solution conditions according to the actual in-situ stress conditions and reservoir environment of the shale gas reservoir. When the initial in-situ stress is balanced according to the definite solution conditions, combined with the fluid-solid coupling model for shale gas reservoirs, analyze the influence of the fluid layer on the solid layer and the influence of the solid layer on the fluid layer; Step S30: Calculate the shale gas permeability by combining the influence of the fluid layer on the solid layer and the influence of the solid layer on the fluid layer.

2. The method for constructing a shale gas permeability calculation model based on PD-FDM coupling according to claim 1, wherein The method of coupling peridynamics and the finite difference method to construct a fluid-solid coupling model for shale gas reservoirs is as follows: Establish a solid layer: Establish the solid skeleton in the central area of the fractured shale based on peridynamics, and model the shale reservoir at the boundary based on the finite element method; Establish a fluid layer: Establish a fluid layer that depicts the action of the fluid in the pores of the shale based on the finite difference method; Establish a transition layer: The transition layer is arranged between the fixed layer and the fluid layer, and the transition layer is inserted into the coupling interface of the fluid layer-solid layer to perform parameter interaction.

3. A method for constructing a shale gas permeability calculation model based on PD-FDM coupling according to claim 2, characterized in that The method of analyzing the influence of the fluid layer on the solid layer is as follows: Shale is a porous medium, and the change in the fluid pressure in its pores will cause the deformation and stress redistribution of the shale matrix. In the possible fracture generation area described by peridynamics, the fluid layer grids and the material points of the solid layer with the same scale correspond to each other. Through the transition layer, combine the seepage model to calculate the pore pressure and saturation of the shale, and transfer the shale pore pressure and the saturation to the corresponding material points to correct the deformation parameters of the solid layer; In the far-field area described by the finite element method as the boundary weakens the influence of the boundary conditions, larger finite elements correspond to multiple fluid layer grids, the grid centers correspond to the finite element nodes, and the seepage parameter value of each finite element is the average value of the seepage parameters of the corresponding number of grid nodes.

4. A method for constructing a shale gas permeability calculation model based on PD-FDM coupling according to claim 3, characterized in that, The method of analyzing the influence of the solid layer on the fluid layer is as follows: In the possible fracture generation area described by peridynamics, the fluid layer grids and the material points of the solid layer with the same scale correspond to each other. Through the transition layer, the volume strain obtained by the material points from the stress field is used to correct the porosity and permeability values of the corresponding fluid layer grids; In the far-field area described by the finite element method as the boundary weakens the influence of the boundary conditions, it is transferred from the finite element to the fluid layer grid, and at this time the transition layer is controlled by the finite difference grid.

5. A method for constructing a shale gas permeability calculation model based on PD-FDM coupling according to claim 4, characterized in that Based on the influence of the fluid layer on the solid layer and the influence of the solid layer on the fluid layer, the method of calculating the shale gas permeability is as follows: Combine the peridynamics damage field to divide the area in the fluid-solid coupling model of the shale gas reservoir into a solid domain, a transition domain, and a fracture domain; Calculate the shale gas permeabilities corresponding to the solid domain, the transition domain, and the fracture domain according to the influence of the fluid layer on the solid layer and the influence of the solid layer on the fluid layer. The calculation method of shale gas permeability in the solid domain is as follows: when only elastic deformation occurs in the solid domain without damage or fracture, the permeability of the fluid grid nodes corresponding to the finite element region remains unchanged. Therefore, the permeability of the rock matrix is the shale gas permeability in the solid domain. The calculation method of shale gas permeability in the transition domain is as follows: construct a linear function according to the division index corresponding to the transition domain; based on the linear function, obtain the shale gas permeability in the transition domain from the permeability difference between the solid domain and the fracture domain. The calculation method of shale gas permeability in the fracture domain is as follows: based on the fracture aperture, obtain the shale gas permeability in the fracture domain through the cubic law.

6. The method for constructing a shale gas permeability calculation model based on PD-FDM coupling according to claim 5, wherein Taking the peridynamic damage field as the basis, the region in the shale gas reservoir fluid-solid coupling model is divided into a solid domain, a transition domain, and a fracture domain. The method is as follows: where χ r and χ f are set partitioning indices, representing the characterization quantity of the peridynamic damage field.

7. A system for constructing a shale gas permeability calculation model based on PD-FDM coupling, which is used to calculate the shale gas permeability, is characterized in that The system includes: A model construction module configured to couple peridynamics and the finite difference method to construct a shale gas reservoir fluid-solid coupling model; the shale gas reservoir fluid-solid coupling model includes a solid layer, a fluid layer, and a transition layer. An influence analysis module configured to set the definite solution conditions according to the actual in-situ stress conditions and reservoir environment of the shale gas reservoir; when the initial in-situ stress is balanced according to the definite solution conditions, analyze the influence of the fluid layer on the solid layer and the influence of the solid layer on the fluid layer in combination with the shale gas reservoir fluid-solid coupling model. A permeability calculation module configured to calculate the shale gas permeability in combination with the influence of the fluid layer on the solid layer and the influence of the solid layer on the fluid layer.

8. An electronic device, characterized in that, It includes: At least one processor; And a memory communicatively connected to at least one of the processors; Wherein, the memory stores instructions executable by the processor, and the instructions are used to be executed by the processor to implement a method for constructing a shale gas permeability calculation model based on PD-FDM coupling according to any one of claims 1-6.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions, and the computer instructions are used to be executed by the computer to implement a method for constructing a shale gas permeability calculation model based on PD-FDM coupling according to any one of claims 1-6.

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