Fluid-solid coupling numerical simulation method and device based on embedded discrete fracture model

Abstract

The present application discloses a fluid-solid coupling numerical simulation method and device based on an embedded discrete fracture model. The reservoir matrix is ​​divided by structured grids, and a discrete fracture model is embedded to construct a geological grid for oil and gas reservoirs. A transfer function is established, and the porous media fluid seepage control equation is formulated accordingly. The equation is solved at each time node to obtain the pore pressure field, and the equivalent pore pressure field is obtained by weighted average as the boundary condition of the solid mechanics control equation. The geological grid model of the oil and gas reservoir is expanded, and the solid mechanics control equation is constructed by combining the fracture-rock constitutive model, the effective stress principle and the stress equilibrium equation. The finite element method and the Newton-Raphson method are used to solve and simulate rock deformation. Based on the constitutive relationship of the composite material, the matrix and fracture seepage properties are updated, and the interaction between the seepage field and the stress field is considered through iterative coupling to achieve multi-field coupling simulation. The problem that the existing methods cannot be applied to real oil and gas reservoirs is solved.

Description

Technical Field

[0001] The present application relates to the technical field of reservoir numerical simulation, and in particular to a fluid-solid coupling numerical simulation method and device based on an embedded discrete fracture model. Background Art

[0002] At present, the numerical simulation methods of fluid-solid coupling for fractured oil and gas reservoirs are mainly divided into two types: those without considering fractures and those with considering fractures. Without considering fractures, the reservoir stress field is regarded as continuous, and the fluid-solid coupling simulation is achieved by establishing the relationship between pore pressure or geostress and reservoir permeability and porosity. However, this method ignores the profound influence of fractures on the reservoir stress field and fluid flow field, so there are limitations in prediction accuracy. When considering fractures, the presence of fractures enhances the heterogeneity and anisotropy of the reservoir stress field, which brings great challenges to numerical simulation. The numerical simulation methods for dealing with fracture effects are mainly based on two frameworks: equivalent medium model and discrete fracture model. Although the equivalent medium model can reflect the influence of fractures to a certain extent, it lacks a description of the specific direction of the fracture and is usually only applicable to the simulation of small-sized natural fractures. The discrete fracture model includes DFM (discrete fracture model) and EDFM (embedded discrete fracture model). DFM requires mesh encryption, which increases the computational cost and the complexity of model establishment, so it is generally not used in fluid-solid coupling numerical simulation. In contrast, the EDFM model has attracted much attention due to its high accuracy and high efficiency.

[0003] However, although the existing methods can accurately simulate the dynamic evolution of fractures, they require local mesh encryption around the fractures or introduce additional degrees of freedom and numerical processing, which results in complex algorithms and high computational costs. In addition, the existing methods are only applicable to two-dimensional models or simple fracture models and cannot be applied to real oil and gas reservoirs. Summary of the invention

[0004] In an embodiment of the present application, a fluid-solid coupling numerical simulation method based on an embedded discrete fracture model is provided to solve the problem that although the existing methods can accurately simulate the dynamic evolution process of fractures, they need to perform local grid encryption processing around the fractures or introduce additional degrees of freedom and numerical processing, resulting in complex algorithms and high computational costs, and are only applicable to two-dimensional models or simple fracture models, and cannot be applied to real oil and gas reservoirs.

[0005] In the first aspect, an embodiment of the present application provides a fluid-solid coupling numerical simulation method based on an embedded discrete fracture model, comprising: using structured grid technology to divide the reservoir matrix to obtain a matrix grid, embedding the discrete fracture model into the matrix grid, and obtaining an oil and gas reservoir geological grid model; establishing a transmission function between the matrix and the fracture according to the fluid exchange mechanism between the fracture and the matrix; establishing a porous medium fluid seepage control equation based on the transmission function between the matrix and the fracture; wherein the porous medium fluid seepage control equation includes a porous medium seepage control equation for the gas phase and the water phase in the matrix and a fracture seepage control equation for the gas phase and the water phase in the fracture; at each time node, in combination with the oil and gas reservoir geological grid model, solving the porous medium fluid seepage control equation to obtain the pore pressure field of the matrix and the fracture in the formation; calculating the weighted average of the matrix pressure and the fracture pressure by the volume weighted average method to obtain an equivalent pore pressure field, and converting the equivalent pore pressure field into the equivalent pore pressure field. The pressure field is used as the boundary condition of the solid mechanics control equation; the geological grid model of the oil and gas reservoir is expanded, the overlying stratum grid, the underlying stratum grid and the lateral stratum grid are expanded, and the corresponding mechanical properties are assigned to the expanded stratum grid to obtain the ground stress grid model; the mechanical properties of the fracture are equivalent to the increase of the unit flexibility by using the flexibility superposition method to construct the fracture-rock constitutive model, and the solid mechanics control equation is constructed by combining the effective stress principle, the fracture-rock constitutive model and the stress equilibrium equation; the solid mechanics control equation is iteratively solved by the finite element discretization method and the Newton-Raphson method to obtain the strain, displacement and effective stress to simulate the deformation behavior of the rock during the oil and gas extraction process; based on the constitutive relationship of the composite material, the strain of the matrix and the fracture is calculated, and the seepage properties of the fracture and the matrix are calculated and updated based on the strain of the matrix and the fracture for seepage field calculation; based on the iterative coupling method, the coupling effect between the seepage field and the stress field is considered.

[0006] In a possible implementation, the method further includes: setting the seepage parameters of the reservoir, setting the initial conditions of the reservoir, and setting the development strategy.

[0007] In a possible implementation, the mechanical properties of the fracture are equivalent to the increase of unit flexibility by using the flexibility superposition method to construct a fracture-rock constitutive model, including: the expression of the fracture-rock constitutive model is: ;in, is the effective stress, is the dependent variable, is the flexibility matrix of the matrix material, which is used to describe the flexibility characteristics of crack-free rock. is the flexibility matrix of the fracture material, which combines the flexibility characteristics of the fracture and the influence of the anisotropic elastic modulus of the rock caused by the fracture. is the volume fraction of the matrix material, is the volume fraction of crack material, is the equivalent stiffness.

[0008] In a possible implementation, the effective stress principle, the fracture-rock constitutive model and the stress balance equation are combined to construct the solid mechanics control equation, including: the effective stress principle is: in a porous medium, the total stress is decomposed into two parts: effective stress and pore pressure; the stress balance equation describes the equilibrium state of stress inside the rock; the strain relationship equation links the strain variable with the displacement field; the expression of the solid mechanics control equation is: ;in, is the equivalent stiffness, is the spatial gradient, is the displacement field, is the expression of the dependent variable, is the biot coefficient, is the pore pressure, is the identity matrix, is the body density vector, is the transpose operation.

[0009] In a possible implementation, the method further includes: using the initial geostress field as an initial condition to initialize the static equilibrium of the geostress field before calculating the weighted average value of the matrix pressure and the fracture pressure by the volume weighted average method to obtain the equivalent pore pressure field and using the equivalent pore pressure field as the boundary condition of the solid mechanics control equation.

[0010] In a possible implementation, the initial geostress field is expressed by three stresses, namely, vertical stress, minimum horizontal principal stress and maximum horizontal principal stress, and the direction of the minimum horizontal principal stress.

[0011] In a possible implementation, the weighted average of matrix pressure and fracture pressure is calculated by volume weighted average method to obtain equivalent pore pressure field, including: according to the formula Calculate the weighted average of matrix pressure and fracture pressure to obtain the equivalent pore pressure field; where, is the equivalent pore pressure field, is the matrix pressure, is the crack pressure, For the entire computational domain, is the volume element, Represents volume Perform integration.

[0012] In a possible implementation, the calculation of the strain of the matrix and the crack based on the constitutive relationship of the composite material includes: according to the constitutive relationship of the composite material, the matrix and the crack are regarded as a whole, and the strain thereof is the superposition of the strain of the matrix and the crack; using the constitutive relationship of the composite material and the strain relationship, respectively calculating the strain of the matrix and the crack in three orthogonal directions; wherein the strain relationship is defined as the strain of the matrix and the crack being the sum of the strains in the three orthogonal directions.

[0013] In a possible implementation, the calculation and updating of the seepage properties of the fracture and the matrix based on the strain of the matrix and the fracture includes: the seepage properties of the fracture include the normal strain of the fracture and the permeability of the fracture; the seepage properties of the matrix include the porosity of the matrix and the permeability of the matrix; according to the formula Calculate the normal strain of the crack; where, is the normal stress of the crack, is the initial normal stress of the crack, is the normal strain of the crack, is the normal flexibility coefficient of the crack; according to the formula Calculate the updated crack opening; where, is the updated opening of the crack, is the initial opening of the crack; according to the formula Calculate the permeability of the fracture; where, is the permeability of the fracture; the volume strain of the matrix is ​​the sum of the strains of the matrix in three orthogonal directions; according to the formula Calculate the porosity of the updated matrix; where, is the volume strain of the matrix, is the original porosity of the matrix, is the original permeability of the matrix, is the porosity of the updated matrix; according to the formula Calculate the permeability of the updated matrix; where, is the original permeability of the matrix, is the permeability of the updated matrix, is the empirical coefficient.

[0014] In the second aspect, the embodiment of the present application provides a fluid-solid coupling numerical simulation device based on an embedded discrete fracture model, including: establishing an oil and gas reservoir geological grid module, which is used to divide the reservoir matrix using structured grid technology to obtain a matrix grid, embed the discrete fracture model into the matrix grid, and obtain an oil and gas reservoir geological grid model; establishing a transfer function module, which is used to establish a transfer function between the matrix and the fracture according to the fluid exchange mechanism between the fracture and the matrix; establishing a control equation module, which is used to establish a porous medium fluid seepage control equation based on the transfer function between the matrix and the fracture; wherein the porous medium fluid seepage control equation includes a porous medium seepage control equation for the gas phase and the water phase in the matrix and a fracture seepage control equation for the gas phase and the water phase in the fracture; a seepage control equation solving module, which is used to solve the porous medium fluid seepage control equation at each time node in combination with the oil and gas reservoir geological grid model to obtain the pore pressure field of the matrix and the fracture in the formation; an equivalent pore pressure field obtaining module, which is used to calculate the weighted average of the matrix pressure and the fracture pressure by the volume weighted average method to obtain the equivalent pore pressure field, The equivalent pore pressure field is used as the boundary condition of the solid mechanics control equation; a geostress grid model is constructed to expand the geological grid model of the oil and gas reservoir, expand the overlying stratum grid, the underlying stratum grid and the lateral stratum grid, and assign corresponding mechanical properties to the expanded stratum grid to obtain the geostress grid model; a solid mechanics control equation module is constructed to construct a fracture-rock constitutive model by using the flexibility superposition method to convert the fracture mechanical properties into the increase of unit flexibility, and combine the effective stress principle, the fracture-rock constitutive model and the stress equilibrium equation to construct Solid mechanics control equations; solid mechanics control equation solving module, used to iteratively solve the solid mechanics control equations using finite element discretization method and Newton-Raphson method, to obtain strain, displacement and effective stress, so as to simulate the deformation behavior of rock during oil and gas extraction; seepage parameter updating module, used to calculate the strain of matrix and cracks based on the constitutive relationship of composite materials, calculate and update the seepage properties of cracks and matrix based on the strain of matrix and cracks, and use them for seepage field calculation; based on the iterative coupling method, consider the coupling effect between seepage field and stress field.

[0015] One or more technical solutions provided in the embodiments of the present application have at least the following technical effects:

[0016] The embodiment of the present application provides a fluid-solid coupling numerical simulation method based on an embedded discrete fracture model, which uses structured grid technology to finely divide the reservoir matrix, effectively reducing the complexity and computational cost of grid generation. The discrete fracture model is seamlessly embedded in the matrix grid, without the need for complex local grid encryption processing, which significantly improves the simulation efficiency. According to the fluid exchange mechanism between the fracture and the matrix, the transfer function between the matrix and the fracture is established, and the dynamic balance of the fluid between the matrix and the fracture is achieved. The porous medium seepage control equation containing gas phase and water phase and the fracture seepage control equation are constructed to accurately describe the flow behavior of the fluid in the complex geological structure. The geological grid model of the oil and gas reservoir is expanded to include the overlying strata, the underlying strata and the lateral strata, providing more comprehensive geological structure information for the simulation. The corresponding mechanical properties are given to the extended stratigraphic grid to ensure the accuracy and reliability of the simulation results. The mechanical properties of the fracture are equivalent to the increase of the unit flexibility through the flexibility superposition method, and the constitutive model of the fracture-rock is constructed to achieve an accurate description of the fluid-solid coupling effect. Combining the effective stress principle, the constitutive model of fracture-rock and the stress balance equation, the solid mechanics control equation is constructed, which provides a theoretical basis for simulating the deformation behavior of rocks. At each time node, combined with the ground stress grid model, the porous media fluid seepage control equation is solved to obtain the pore pressure field in the formation. The equivalent pore pressure field is calculated by the volume weighted average method as the boundary condition of the solid mechanics control equation, and the iterative solution of fluid-solid coupling is realized. The finite element discretization method and the Newton-Raphson method are used to efficiently iteratively solve the solid mechanics control equation, and the strain, displacement and effective stress are obtained, which provides data support for simulating the deformation behavior of rocks during oil and gas production. The strain of the matrix and the fracture can be calculated through the constitutive relationship of the composite material. It helps to deeply understand the microscopic deformation mechanism of the material under complex stress environment, so as to improve the prediction accuracy of the overall mechanical properties of the material. The seepage properties of the fracture and the matrix are calculated and updated based on the strain of the matrix and the fracture. It can reflect the influence of the internal microstructure changes of the material on the seepage characteristics, making the seepage field calculation closer to the actual physical process. The iterative coupling method is adopted to consider the interaction between the seepage field and the stress field. The change of pore pressure caused by seepage will affect the stress state of the material, and the change of stress state will in turn affect the seepage properties. This two-way coupling mechanism can more accurately simulate the complex physical phenomena under the action of multi-field coupling. It solves the problem that although the existing methods can accurately simulate the dynamic evolution process of fractures, they need to perform local mesh encryption around the fractures or introduce additional degrees of freedom and numerical processing, resulting in complex algorithms and high computational costs. In addition, they are only applicable to two-dimensional models or simple fracture models and cannot be applied to real oil and gas reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments of the present application or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 A flow chart of a fluid-solid coupling numerical simulation method based on an embedded discrete fracture model provided in an embodiment of the present application;

[0019] Figure 2 A schematic diagram of a geological grid model of an oil and gas reservoir provided in an embodiment of the present application;

[0020] Figure 3 A schematic diagram of a geostress grid model provided in an embodiment of the present application;

[0021] Figure 4 A schematic diagram of the pore pressure field distribution after 1000 days of production provided in an embodiment of the present application;

[0022] Figure 5 A schematic diagram of effective stress distribution after 1000 days of production provided in an embodiment of the present application;

[0023] Figure 6 A dynamic curve diagram of daily production and cumulative production of different wells during production provided in the embodiments of the present application;

[0024] Figure 7 A schematic diagram of a curve showing changes in crack aperture and crack permeability over time provided in an embodiment of the present application;

[0025] Figure 8 A schematic diagram of a fluid-solid coupling numerical simulation device based on an embedded discrete fracture model provided in an embodiment of the present application;

[0026] Fig. 9 A schematic diagram of a fluid-solid coupling numerical simulation server based on an embedded discrete fracture model provided in an embodiment of the present application. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0028] The following describes some of the techniques involved in the embodiments of the present application to facilitate understanding, and they should be considered as merely exemplary. Therefore, it should be appreciated by those of ordinary skill in the art that various changes and modifications may be made to the embodiments described herein without departing from the scope and spirit of the present application. Similarly, for the sake of clarity and conciseness, some descriptions of well-known functions and structures are omitted in the following description.

[0029] The present application embodiment provides a fluid-solid coupling numerical simulation method based on an embedded discrete fracture model, such as Figure 1 As shown, the method includes steps S101 to S110. Among them, Figure 1 This is only an execution order shown in the embodiment of the present application, and does not represent the only execution order of a fluid-solid coupling numerical simulation method based on an embedded discrete fracture model. In the case where the final result can be achieved, Figure 1 The steps shown may be performed in parallel or reversed.

[0030] S101: Use structured grid technology to divide the reservoir matrix to obtain a matrix grid, embed the discrete fracture model into the matrix grid, and obtain an oil and gas reservoir geological grid model.

[0031] Specifically, by embedding the discrete fracture model into the matrix grid, the interaction and fluid exchange relationship between the fracture and the matrix can be described more accurately.

[0032] The application also includes: setting the seepage parameters of the reservoir, setting the initial conditions of the reservoir, and setting the development strategy.

[0033] Specifically, in order to simulate the flow behavior of the fluid in the reservoir, a series of seepage parameters need to be set. These parameters include: PVT curve (pressure-volume-temperature curve), which is used to describe the changes in the physical properties of the fluid at different pressures and temperatures. Phase permeability curve, which is used to describe the flow characteristics of the fluid in the reservoir pores and the relative permeability of the fluid in the reservoir. Rock compression coefficient, which is used to describe the volume change of the reservoir rock under pressure changes. In order to simulate the initial state of the reservoir, a series of initial conditions need to be set. These conditions include: setting the initial saturation distribution of the fluid in the reservoir to reflect the fluid content and distribution state of the reservoir. Determine the initial reservoir pressure of the reservoir to reflect the pressure state and fluid flow potential of the reservoir. Determine the position of the gas-water interface in the reservoir to distinguish the areas of gas reservoirs and water reservoirs. It should be noted that the fluid in this application includes gas phase and water phase.

[0034] S102: Establishing a transfer function between the matrix and the fracture according to the fluid exchange mechanism between the fracture and the matrix.

[0035] Specifically, in order to accurately describe the fluid exchange mechanism between fractures and matrix, it is necessary to establish a transfer function between matrix and fractures. This function can quantify the rate and direction of fluid flow between fractures and matrix, and is the key to simulating the flow behavior of fluids in complex oil and gas reservoirs.

[0036] Specifically, it is assumed that the exchange rate between the gas phase and the water phase can be described by the transport coefficients. These transport coefficients represent the transport capacity of the gas phase and the water phase from the matrix to the fracture, respectively. They reflect the flow characteristics and permeability of the fluid at the interface between the fracture and the matrix.

[0037] For the gas phase, the transfer function can be expressed as: .in, is the exchange rate of gas phase between fractures and matrix, that is, the mass or volume of fluid passing through unit area per unit time, is the transmission coefficient of the gas phase, is the pressure of the gas phase in the matrix, is the pressure of the gas phase in the fracture. For the water phase, the transfer function can be expressed as: .in, is the exchange rate of water phase between fractures and matrix, that is, the mass or volume of fluid passing through unit area per unit time, is the transmission coefficient of the water phase, is the pressure of the aqueous phase in the matrix, is the pressure of water phase in the fracture.

[0038] S103: Establishing a porous medium fluid seepage control equation based on the transfer function between the matrix and the fracture, wherein the porous medium fluid seepage control equation includes a porous medium seepage control equation for the gas phase and water phase in the matrix and a fracture seepage control equation for the gas phase and water phase in the fracture.

[0039] Based on the transmission function between the matrix and the fracture, the porous media fluid seepage control equation is established, including: the transmission function between the matrix and the fracture includes the transmission function of the gas phase and the transmission function of the water phase. Among them, the transmission function of the gas phase is used to describe the exchange rate of the gas phase between the fracture and the matrix, and the transmission function of the water phase is used to describe the exchange rate of the water phase between the fracture and the matrix. The exchange rate between the gas phase and the water phase between the fracture and the matrix is ​​calculated by the transmission function, and the exchange rate is used as the exchange term. The exchange term is combined with the source term to establish the porous media fluid seepage control equation.

[0040] Specifically, in order to comprehensively describe the seepage behavior of fluids in the matrix and fractures, the porous media fluid seepage control equations are constructed based on Darcy's theorem and the mass conservation equation, combined with the phase equilibrium equation, the state equation, and the previously established transfer function between the matrix and the fracture. That is, the porous media seepage control equations for the gas phase and water phase in the matrix and the fracture seepage control equations for the gas phase and water phase in the fracture.

[0041] For the gas phase and water phase in the matrix, the seepage control equations were established respectively, namely the porous media seepage control equation for the gas phase in the matrix and the porous media seepage control equation for the water phase in the matrix. These equations take into account factors such as fluid saturation, density, viscosity, permeability, porosity, and gravity effect. At the same time, the exchange rate calculated by introducing the transfer function is included in the equation as an exchange term to reflect the fluid exchange between the fracture and the matrix.

[0042] The expression of the porous media seepage control equation for the gas phase in the matrix is: .in, For time The partial derivative of is the porosity, is the gas phase saturation, is the gas phase density, is the gradient operator, is the absolute permeability of the medium, is the relative permeability of the gas phase, is the gas phase viscosity, is the pressure of the gas phase in the matrix, is the gravity on the gas phase, is the gas source term in the matrix, which represents the external injection or extraction rate of gas in the porous medium per unit volume per unit time. It is the gas exchange term, which indicates the exchange rate of gas between fractures and matrix, that is, the mass or volume of fluid passing through unit area per unit time.

[0043] The expression of the porous media seepage control equation for the water phase in the matrix is: .in, is the water phase saturation, is the density of water phase, is the relative permeability of the water phase, is the viscosity of the water phase, is the gradient operator, is the pressure of the aqueous phase in the matrix, is the gravity acting on the water phase, is the source term of water phase in the matrix, which represents the external injection or extraction rate of water phase in unit volume of porous medium per unit time. It is the water phase exchange term, which indicates the exchange rate of water phase between fractures and matrix, that is, the mass or volume of fluid passing through unit area per unit time.

[0044] The auxiliary equations include the equation for saturation summing to 1 , and the phase equilibrium equation between the gas phase and the water phase .in, is the capillary pressure.

[0045] Similarly, seepage control equations are established for the gas phase and water phase in the fracture, namely the fracture seepage control equation for the gas phase in the fracture and the fracture seepage control equation for the water phase in the fracture. These equations take into account factors such as the permeability and porosity of the fracture and the relative permeability of the fluid in the fracture. At the same time, the exchange rate calculated by introducing the transfer function is included in the equation as an exchange term to reflect the fluid exchange between the fracture and the matrix.

[0046] The expression of the fracture seepage control equation for the gas phase in the fracture is: .in, is the porosity of the fracture, is the gas saturation in the fracture, is the gradient operator in the crack plane, is the permeability of the fracture, is the relative permeability of the gas phase in the fracture, is the pressure of the gas phase in the crack, is the gas source term in the fracture, which represents the external injection or extraction rate of gas in the fracture per unit volume per unit time.

[0047] The expression of the fracture seepage control equation for the water phase in the fracture is: .in, is the water saturation in the fracture, is the relative permeability of water phase in the fracture, is the pressure of water phase in the fracture, is the water phase source term in the fracture, which represents the external injection or extraction rate of gas phase in the fracture per unit volume per unit time.

[0048] In order to solve the above porous media fluid seepage control equation, the finite difference method is used for numerical discretization. By expressing the derivative terms in the equation in differential form, the continuous equation can be converted into a discrete equation for solution. In terms of time discretization, an implicit solution method is used. This method can overcome the stability limitations of the explicit method by solving the unknown quantity within the current time step, allowing the use of a larger time step for simulation. For nonlinear problems in the equation (such as the nonlinear relationship between relative permeability and saturation), the Newton-Raphson method is applied for iterative solution. By continuously iteratively updating the value of the unknown quantity vector, the solution of the equation can be gradually approached, thereby obtaining accurate simulation results.

[0049] It should be noted that the pore pressure field in the present application includes the pressure of the gas phase in the matrix, the pressure of the water phase in the matrix, the pressure of the gas phase in the fractures, and the pressure of the water phase in the fractures.

[0050] Specifically, in the above equation, the iteration process of the Newton-Raphson method can be expressed as the following two steps: 1. Construct the Jacobian matrix and solve the linear equations. In each iteration, the current unknown vector , to calculate the residual of the nonlinear system of equations In the seepage problem, the unknown quantity vector Variables such as pressure and saturation can be included. Construct the Jacobian matrix , which contains the equations for the unknown vector Solve the following linear system to find the increment : This system of equations expresses the unknown vector At , we use linear approximation to find the direction that reduces the residual, that is, to solve the increment that can make the equation system closer to the true solution. 2. Update the unknown vector. Once the increment is found , which can be used to update the unknown vector and obtain a new approximate solution : The new approximate solution Than the previous solution, that is, the unknown vector Closer to the true solution.

[0051] S104: At each time node, combined with the oil and gas reservoir geological grid model, solve the porous medium fluid seepage control equation to obtain the pore pressure field of the matrix and fractures in the formation.

[0052] Specifically, in the process of oil and gas reservoir simulation, in order to more accurately predict the fluid dynamics and geostress field changes of the oil and gas reservoir, a series of calculations need to be performed at each time node in combination with the geostress grid model. The geostress grid model is used as the basic framework for calculation. This model contains key parameters such as the geological structure, lithology distribution, porosity, and permeability of the oil and gas reservoir, and is an important basis for simulating fluid flow. By solving this porous medium fluid seepage control equation, the pore pressure field in the formation can be obtained. Pore pressure is an important parameter of oil and gas reservoir fluid dynamics, which reflects the distribution state and flow trend of the fluid in the formation. After obtaining the pore pressure field, it is used as a boundary condition to calculate the change of the geostress field. Geostress is an important indicator of the mechanical properties of oil and gas reservoir rocks, which determines the deformation, fracture, and oil and gas migration processes of rocks. When calculating the change of the geostress field, the influence of pore pressure on the stress of the rock skeleton is considered. Due to the existence of pore pressure, the stress borne by the rock skeleton will change, resulting in the redistribution of geostress. By simulating this change, we can more accurately understand the mechanical state of the rock in the oil and gas reservoir, providing strong support for the exploration and development of the oil and gas reservoir. It should be noted that the above process requires iterative calculations at each time node. Over time, the fluid dynamics and geostress field of the oil and gas reservoir will change. Therefore, it is necessary to continuously update the parameters in the geostress grid model.

[0053] S105: Calculate the weighted average of the matrix pressure and the fracture pressure by using the volume weighted average method to obtain an equivalent pore pressure field, and use the equivalent pore pressure field as the boundary condition of the solid mechanics control equation.

[0054] Specifically, since the geostress grid model contains both the matrix grid and the discrete fracture model, the calculation results will produce two different sets of pore pressure fields. One set comes from the matrix grid and the other comes from the discrete fracture model. In order to unify these two sets of pore pressure fields into an equivalent pore pressure field, a specific calculation method is required. Specifically: the weighted average of the matrix pressure and the fracture pressure is calculated by the volume weighted average method to obtain the equivalent pore pressure field. According to the formula Calculate the weighted average of matrix pressure and fracture pressure to obtain the equivalent pore pressure field. is the equivalent pore pressure field, is the matrix pressure, is the crack pressure, For the entire computational domain, is the volume element, Represents volume Perform integration.

[0055] The weighted average values ​​of matrix pressure and fracture pressure are calculated by volume weighted average method to obtain equivalent pore pressure field. Before using the equivalent pore pressure field as the boundary condition of solid mechanics control equation, the method also includes: using the initial geostress field as the initial condition to initialize the static balance of the geostress field.

[0056] The initial geostress field is expressed by three stresses: vertical stress, minimum horizontal principal stress and maximum horizontal principal stress, as well as the direction of the minimum horizontal principal stress. It should be noted that the initial geostress field needs to be expressed by adding a stress direction, which can be the direction of the maximum horizontal principal stress. The direction of the maximum horizontal principal stress can be comprehensively determined by methods such as well logging interpretation, hydraulic fracturing testing and structural analysis.

[0057] The calculation of vertical stress is completed by a rock density integral formula. According to the formula Determine the vertical stress. Where, is the vertical stress, To express the density of rock at different depths, is the acceleration due to gravity, is the lower bound of the integral, indicating the depth of the ground. is the upper bound of the integral, indicating the depth position of the calculated vertical stress, Indicates the increment in the depth direction.

[0058] According to the formula Determine the maximum horizontal principal stress according to the formula Determine the minimum horizontal principal stress. Where, is the maximum horizontal principal stress, is the minimum horizontal principal stress, is the biot coefficient, is the pore pressure, is the elastic modulus, is the maximum horizontal strain, is the minimum horizontal strain, is Poisson's ratio, is the vertical stress.

[0059] S106: Expanding the oil and gas reservoir geological grid model, expanding the overlying stratum grid, the underlying stratum grid and the lateral stratum grid, assigning corresponding mechanical properties to the expanded stratum grid, and obtaining a geostress grid model.

[0060] Specifically, in order to simulate the solid mechanical behavior of the stratum, it is necessary to constrain the normal displacement of the boundary grid nodes of the overlying stratum. This ensures that the boundary conditions of the stratum are correctly set in the solid mechanics analysis, thereby more accurately reflecting the actual mechanical behavior of the stratum. The corresponding mechanical properties assigned to the extended stratum grid include Young's modulus, Poisson's ratio, compressive strength, porosity, biot coefficient, rock density, etc. These properties are key parameters for describing the mechanical behavior of the stratum.

[0061] S107: By adopting the flexibility superposition method, the mechanical properties of the fracture are equivalent to the increase of the unit flexibility to construct the fracture-rock constitutive model. Combining the effective stress principle, the fracture-rock constitutive model and the stress equilibrium equation, the solid mechanics control equation is constructed.

[0062] By using the flexibility superposition method, the mechanical properties of the fracture are equivalent to the increase of the unit flexibility to construct the fracture-rock constitutive model, including: The expression of the fracture-rock constitutive model is: .in, is the effective stress, is the dependent variable, is the flexibility matrix of the matrix material, which is used to describe the flexibility characteristics of crack-free rock. is the flexibility matrix of the fracture material, which combines the flexibility characteristics of the fracture and the influence of the anisotropic elastic modulus of the rock caused by the fracture. is the volume fraction of the matrix material, is the volume fraction of crack material, is the equivalent stiffness.

[0063] Specifically, the presence of cracks has a significant impact on the reservoir in-situ stress field and displacement field. Cracks enhance the heterogeneity and anisotropy of the reservoir in-situ stress field, making the stress distribution more complicated. At the same time, in areas where cracks exist, there is discontinuity in the displacement field, that is, the displacements on both sides of the cracks may change suddenly. Traditional numerical simulation methods, such as conventional finite element method and finite volume method, face challenges in simulating the effects of cracks on the reservoir in-situ stress field and displacement field. These methods are difficult to accurately capture complex phenomena such as stress concentration and displacement discontinuity caused by cracks. In order to overcome this problem, the present application equates cracks to an increase in unit flexibility, and equates the mechanical properties of cracks to anisotropic elastic moduli. Through this method, the effect of cracks on rock stiffness can be simulated, thereby more accurately predicting the distribution of reservoir in-situ stress field and displacement field. Specifically, the flexibility matrix is ​​introduced and the stiffness matrix The relationship between The presence of cracks will increase the overall flexibility and reduce the corresponding stiffness. Therefore, when constructing the crack-rock constitutive model, the flexibility matrix of the crack material is considered. Effect on overall flexibility. Equivalent stiffness The contribution of matrix material and crack material to the overall stiffness is combined. For anisotropic materials, the equivalent stiffness can be expressed as Matrix. This method can more accurately simulate the impact of fractures on reservoir stress and displacement fields, providing strong support for the exploration and development of oil and gas reservoirs. At the same time, this method also provides new ideas and methods for the numerical simulation of fractured reservoirs.

[0064] Combining the effective stress principle, the fracture-rock constitutive model and the stress balance equation, the solid mechanics control equations are constructed, including: The effective stress principle is: In porous media, the total stress is decomposed into two parts: effective stress and pore pressure. The stress balance equation describes the equilibrium state of stress inside the rock. The strain relationship equation links the strain variable with the displacement field.

[0065] The governing equations of solid mechanics are expressed as: .in, is the equivalent stiffness, is the spatial gradient, is the displacement field, is the expression of the dependent variable, is the biot coefficient, is the pore pressure, is the identity matrix, is the body density vector, is the transpose operation.

[0066] Specifically, in order to deeply understand and simulate the solid mechanical behavior of fractured reservoirs, the solid mechanics control equations were constructed by combining the effective stress principle, the fracture-rock constitutive model and the stress equilibrium equation.

[0067] In a porous medium environment, the total stress includes not only the stress borne by the rock skeleton, but also the influence of the pore fluid pressure. According to the effective stress principle, the total stress It can be decomposed into effective stress and pore pressure The relationship between them is expressed as follows: .in, is the biot coefficient, is the unit matrix. Inside the rock, the stress distribution must satisfy the equilibrium condition, that is, the divergence of the stress tensor and the body density vector The sum of the stresses (such as gravity) is zero. The stress equilibrium equation can be expressed as: There is a direct mathematical relationship between the strain and the displacement field. Through the strain relationship equation, the strain can be expressed as the symmetric part of the displacement field gradient, that is: .in, is the dependent variable.

[0068] S108: Finite element discretization method and Newton-Raphson method are used to iteratively solve the solid mechanics control equations to obtain strain, displacement and effective stress to simulate the deformation behavior of rocks during oil and gas production.

[0069] Specifically, in the solid mechanics simulation, in order to solve the deformation behavior of rocks during oil and gas extraction, the finite element discretization method and the Newton-Raphson method are used for iterative solution. The following is a detailed description of this step. The displacement field is interpolated using the standard finite element method. and pore pressure is represented as a linear combination of node values. Specifically, the displacement field It can be expressed as a shape function On a single grid node The value on the node displacement The product of Similarly, the pore pressure It can be expressed as a shape function On a single grid node The value on the node pressure vector The product of It should be noted that in this step, the node refers to the grid node.

[0070] Based on the relationship between strain and displacement, the expression of strain quantity is derived. It can be expressed as .in, is the strain-displacement matrix, is the node displacement. In order to solve the solid mechanics governing equation, a potential energy function needs to be constructed. Substituting the stress-strain relationship into the stress equilibrium equation and combining the influence of pore pressure, an integral equation for displacement and pore pressure can be obtained. The integral equation for displacement and pore pressure is: .in, is the shape function. This integral equation actually describes the integral equation for displacement and pore pressure under the condition that the total potential energy is zero. Through finite element discretization, the above integral equation is organized into a matrix equation: .in, is the stiffness matrix, The contribution of pressure to displacement, , is the external load vector, , is the body density vector, is the transposed matrix of the shape function, is the transposed matrix of the strain-displacement matrix.

[0071] To solve the above matrix equation, the Newton-Raphson method is used for iterative solution. For each iteration, the following steps are performed. Calculate the residual vector , which represents the unbalanced force at the current iteration. . Where n is the number of iterations. Calculate the Jacobian matrix , which describes the derivative of the residual vector with respect to the displacement. .in, is the derivative of the linearized nonlinear system, i.e., the Jacobian matrix, Residual vector Displacement The derivative of is the displacement The stiffness matrix of is the contribution of pore pressure to the stiffness matrix, which is also the displacement function.

[0072] In each iteration, the following steps are performed to solve for the displacement.

[0073] Step 1: Calculate the tangent stiffness matrix. The tangent stiffness matrix is The tangent stiffness matrix is It is obtained by differentiating the displacement term, and it describes the response to a small displacement change under the current displacement state. .

[0074] Step 2: Construct and solve the update equations. Use the tangent stiffness matrix , construct the following update equation: Solving this equation, we get the displacement increment .

[0075] Step 3: Update the displacement. Use the displacement increment Update the displacement. .in, is the displacement in the current iteration, is the updated displacement.

[0076] Step 4: Check convergence. Check the residual vector at the current iteration Is the norm of less than the preset threshold? If this condition is met, it is considered converged and the iteration process stops. Otherwise, return to step 1 and continue the next iteration.

[0077] S109: Based on the constitutive relationship of the composite material, the strains of the matrix and the cracks are calculated. Based on the strains of the matrix and the cracks, the seepage properties of the cracks and the matrix are calculated and updated for seepage field calculation.

[0078] S110: Based on the iterative coupling method, the coupling effect between the seepage field and the stress field is considered.

[0079] Based on the constitutive relationship of the composite material, the strain of the matrix and the crack is calculated, including: according to the constitutive relationship of the composite material, the matrix and the crack are regarded as a whole, and the strain is the superposition of the strain of the matrix and the crack. The strain of the matrix and the crack in three orthogonal directions is calculated respectively by using the constitutive relationship of the composite material and the strain relationship. Among them, the strain relationship is defined as the strain of the matrix and the crack is the sum of the strains in the three orthogonal directions.

[0080] Since the result of solid mechanics calculation is the result of equivalent treatment of cracks in the form of flexibility superposition, auxiliary formulas are needed to accurately calculate the strain of the matrix and cracks. The strain of the matrix and cracks is expressed as the sum of the strains in three orthogonal directions, that is, .in, is the dependent variable, , and They represent the strains in three orthogonal directions respectively.

[0081] The meshes of the crack and matrix can be equivalent to composite materials. The strains in the three orthogonal directions can be expressed as the sum of the strains of the matrix and the crack, respectively, and the constitutive relation of the composite material is obtained: .in, , and are the strains of the matrix in three orthogonal directions, , and are the strains of the crack in three orthogonal directions. According to the constitutive relationship of the composite material, in the x direction: , Combining the above formula, we can solve the strain of matrix and crack in x direction, and the strain in y and z direction can be obtained in the same way.

[0082] The normal stress of the crack is calculated based on the normal strain of the crack and the constitutive relationship of the composite material. The normal strain of the crack can be obtained by The normal stress of the crack can be calculated by the constitutive relationship: .in, , and are the cosine values ​​of the angles between the unit vectors in these three orthogonal directions and the crack normal direction, is the normal strain of the crack, is the normal stress of the crack, is the normal flexibility coefficient of the crack.

[0083] Based on the strain of the matrix and the fracture, the seepage properties of the fracture and the matrix are calculated and updated, including: the seepage properties of the fracture include the normal strain of the fracture and the permeability of the fracture. The seepage properties of the matrix include the porosity of the matrix and the permeability of the matrix. According to the formula Calculate the normal strain of the crack. is the normal stress of the crack, is the initial normal stress of the crack, is the normal strain of the crack, is the normal flexibility coefficient of the crack. According to the formula Calculate the updated crack opening. is the updated opening of the crack, is the initial opening of the crack. According to the formula Calculate the permeability of the fracture. Where, is the permeability of the fracture. The volume strain of the matrix is ​​the sum of the strains of the matrix in three orthogonal directions. According to the formula Calculate the porosity of the updated matrix. Where, is the volume strain of the matrix, is the original porosity of the matrix, is the original permeability of the matrix, is the porosity of the updated matrix. According to the formula Calculate the permeability of the updated matrix. Where, is the original permeability of the matrix, is the permeability of the updated matrix, It is an empirical coefficient, which comes from experimental measurement and data fitting, and is a quantitative description of the sensitivity of a material or system to external factors. In this application, the empirical coefficient can be 0.5, and of course it can be other values, and this application is not limited to this value.

[0084] Furthermore, in each time step, iterative calculations are performed. After each iteration, it is necessary to perform convergence checks on key variables such as the pore pressure field and the geostress field. By comparing the results of the current iteration step with the previous iteration step or the preset convergence criteria, it is determined whether the current iteration has reached convergence. The convergence criteria may include that the change in the variable is less than a certain threshold, the number of iterations reaches a preset upper limit, etc. If the current iteration step does not reach the convergence criteria, it returns to continue iterating until the convergence conditions are met or the maximum number of iterations is reached. Once the current iteration step reaches the convergence criteria, it is considered that the calculation of the time step has been completed, and the time step is updated at this time. The update of the time step can be based on the progress of the simulation, the rate of change of the variables, or other related factors. The results of each field in the current time step, such as the pore pressure field and the geostress field, are used as the initial conditions of the next time step to prepare for the calculation of the next time step. The results of each time step are stored for subsequent analysis and visualization. Visualization tools are used to conduct in-depth analysis of key information such as the seepage field, geostress field, and fracture dynamics to understand the physical phenomena and changing trends during the simulation process. Check whether the simulation reaches the set termination conditions, such as the specified simulation time, number of iterations, etc. If the termination conditions are met, the final simulation results are output and the calculation process ends. If the termination conditions are not met, the calculation of the next time step is continued, and the above iteration, convergence check, time step update, and result storage and analysis steps are repeated until the simulation ends.

[0085] This application selects a shale gas well group model as the research target, and sets the oil and gas reservoir geological grid model size to 2090×1210m, which can accommodate complex geological structures and fluid flow simulations. The reservoir depth ranges from 3375m to 3491m, and the reservoir thickness reaches 116m. Figure 2 A schematic diagram of a geological grid model of an oil and gas reservoir provided in an embodiment of the present application, such as Figure 2 As shown, the gray is the matrix grid and the blue is the fracture. The reservoir is exploited by multi-stage hydraulic fracturing through three horizontal wells, W34-1HF, W34-2HF, and W34-3HF. These three wells are exploited by multi-stage hydraulic fracturing technology, that is, fracturing operations are carried out at different reservoir locations in the wellbore to form multiple fractures, thereby effectively improving the permeability of the reservoir and promoting the flow and exploitation of shale gas. The well group will produce at a fixed production pressure, which means that during the production process, the bottom hole flowing pressure will be maintained at a constant level (3MPa), while the production may vary depending on the changes in reservoir conditions and fluid properties. The planned production is 1000 days, which is a relatively long period of time to fully evaluate the effectiveness of the exploitation strategy and the long-term behavior of the reservoir. Every 100 days is a coupling step. In simulation, coupling steps are usually used to gradually update parameters to reflect dynamic changes in the actual production process.

[0086] Figure 3Schematic diagram of the geostress grid model provided in the embodiment of the present application. Figure 3 As shown, the geostress grid model is obtained by expanding the oil and gas reservoir geological grid model by expanding the overlying stratum grid, the underlying stratum grid and the lateral stratum grid.

[0087] Figure 4 This is a schematic diagram of the pore pressure field distribution after 1000 days of production provided in the embodiment of this application. Figure 4 As shown, the pore pressure is expressed in bar, providing information on the pressure changes in the oil and gas reservoir during production. Figure 4 , it can be found that the pore pressure presents a complex and diverse distribution pattern inside the oil and gas reservoir. These pressure distributions reflect the geological structure of the oil and gas reservoir, the fluid flow characteristics, and the impact of production activities on the reservoir. Specifically, the color changes in different areas represent the changes in the size of the pore pressure, and the change from dark to light colors indicates the trend of pressure from high to low.

[0088] Figure 5 This is a schematic diagram of the effective stress distribution after 1000 days of production provided in the embodiment of the present application. The effective stress in the present application is expressed in units of bar. Figure 5 (a) is the minimum horizontal effective stress distribution after 1000 days of production. Figure 5 (b) in the figure is the maximum horizontal effective stress distribution after 1000 days of production. During the production process, as oil and gas are produced, the pore pressure in the near-well area will gradually decrease. As the pore pressure decreases, the effective stress on the rock will increase accordingly. There is strong heterogeneity and anisotropy. This application can accurately simulate and calculate the effective stress changes near the fracture.

[0089] Figure 6 Dynamic curves of daily production and cumulative production of different wells (WY34-1HF, WY34-2HF and WY34-3HF) during production provided in the embodiments of this application. The time axis is in days, starting from 0 days and going up to 1000 days. This time range covers the production process from the initial stage of production to a longer period of time.

[0090] Figure 7 Schematic diagram of the curves of crack opening and crack permeability over time provided in the embodiments of the present application. The crack opening is the red curve, and the crack permeability is the blue curve. Figure 7 It can be seen that both the crack opening and the crack permeability change with time.

[0091] The present application also provides a fluid-solid coupling numerical simulation device 800 based on an embedded discrete fracture model. Figure 8As shown, the device includes: a module 801 for establishing a geological grid for oil and gas reservoirs, a module 802 for establishing a transfer function, a module 803 for establishing a control equation, a module 804 for solving a seepage control equation, a module 805 for obtaining an equivalent pore pressure field, a module 806 for constructing a geostress grid model, a module 807 for constructing a solid mechanics control equation, a module 808 for solving a solid mechanics control equation, and a module 809 for updating seepage parameters.

[0092] The oil and gas reservoir geological grid establishment module 801 is used to divide the reservoir matrix using the structured grid technology to obtain the matrix grid, embed the discrete fracture model into the matrix grid, and obtain the oil and gas reservoir geological grid model.

[0093] The transmission function establishment module 802 is used to establish a transmission function between the matrix and the fracture according to the fluid exchange mechanism between the fracture and the matrix.

[0094] The control equation establishment module 803 is used to establish a porous medium fluid seepage control equation based on the transfer function between the matrix and the fracture. The porous medium fluid seepage control equation includes a porous medium seepage control equation for the gas phase and water phase in the matrix and a fracture seepage control equation for the gas phase and water phase in the fracture.

[0095] The seepage control equation solving module 804 is used to solve the porous medium fluid seepage control equation at each time node in combination with the oil and gas reservoir geological grid model to obtain the pore pressure field of the matrix and fractures in the formation.

[0096] The module 805 for obtaining the equivalent pore pressure field is used to calculate the weighted average of the matrix pressure and the fracture pressure by the volume weighted average method to obtain the equivalent pore pressure field, and use the equivalent pore pressure field as the boundary condition of the solid mechanics control equation.

[0097] Constructing the geostress grid model 806 is used to expand the oil and gas reservoir geological grid model, expand the overlying stratum grid, the underlying stratum grid and the lateral stratum grid, and assign corresponding mechanical properties to the expanded stratum grid to obtain the geostress grid model.

[0098] The solid mechanics control equation construction module 807 is used to construct the fracture-rock constitutive model by using the flexibility superposition method to equate the fracture mechanical properties to the increase of unit flexibility, and to construct the solid mechanics control equation by combining the effective stress principle, the fracture-rock constitutive model and the stress equilibrium equation.

[0099] The solid mechanics control equation solving module 808 is used to iteratively solve the solid mechanics control equation using the finite element discretization method and the Newton-Raphson method to obtain the strain, displacement and effective stress to simulate the deformation behavior of the rock during the oil and gas production process.

[0100] The seepage parameter update module 809 is used to calculate the strain of the matrix and the crack based on the constitutive relationship of the composite material, calculate and update the seepage properties of the crack and the matrix based on the strain of the matrix and the crack for seepage field calculation. Based on the iterative coupling method, the coupling effect between the seepage field and the stress field is considered.

[0101] Some modules in the apparatus described in the present application can be described in the general context of computer executable instructions executed by a computer, such as program modules. Generally, program modules include routines, programs, objects, components, data structures, classes, etc. that perform specific tasks or implement specific abstract data types. The present application can also be practiced in distributed computing environments, in which tasks are performed by remote processing devices connected through a communication network. In a distributed computing environment, program modules can be located in local and remote computer storage media including storage devices.

[0102] The devices or modules described in the above application embodiments can be implemented by computer chips or entities, or by products with certain functions. For the convenience of description, the above devices are described in various modules according to their functions. When implementing the embodiments of the present application, the functions of each module can be implemented in the same or multiple software and / or hardware. Of course, the module that implements a certain function can also be implemented by combining multiple sub-modules or sub-units.

[0103] The methods, devices or modules described in this application can be implemented in the form of computer-readable program codes. The controller can be implemented in any appropriate manner. For example, the controller can take the form of a microprocessor or processor and a computer-readable medium storing computer-readable program codes (such as software or firmware) that can be executed by the (micro)processor, logic gates, switches, application-specific integrated circuits (English: Application Specific Integrated Circuit, referred to as: ASIC), programmable logic controllers and embedded microcontrollers. Examples of controllers include but are not limited to the following microcontrollers: ARC 625D, Atmel AT91SAM, Microchip PIC18F26K20 and Silicone Labs C8051F320. The memory controller can also be implemented as part of the control logic of the memory. Those skilled in the art also know that in addition to implementing the controller in the form of pure computer-readable program codes, the controller can be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers and embedded microcontrollers by logically programming the method steps. Therefore, this controller can be considered as a hardware component, and the devices included in it for implementing various functions can also be regarded as structures within the hardware component. Or even, the means for realizing various functions may be regarded as both a software module for realizing the method and a structure within a hardware component.

[0104] like Fig. 9 As shown, an embodiment of the present application also provides a fluid-solid coupling numerical simulation server based on an embedded discrete fracture model, including a memory 901 and a processor 902; the memory 901 is used to store computer executable instructions; the processor 902 is used to execute computer executable instructions to implement a fluid-solid coupling numerical simulation method based on an embedded discrete fracture model described above in an embodiment of the present application.

[0105] An embodiment of the present application also provides a computer-readable storage medium, which stores executable instructions. When a computer executes the executable instructions, it can implement the fluid-solid coupling numerical simulation method based on an embedded discrete fracture model described above in the embodiment of the present application.

[0106] It can be seen from the description of the above implementation methods that those skilled in the art can clearly understand that the present application can be implemented by means of software plus necessary hardware. Based on this understanding, the technical solution of the present application can be essentially or partly contributed to the prior art in the form of a software product, or it can be reflected in the implementation process of data migration. The computer software product can be stored in a storage medium, such as ROM / RAM, a disk, an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a mobile terminal, a server, or a network device, etc.) to execute the method described in the embodiment of the present application.

[0107] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. All or part of this application can be used in many general or special computer system environments or configurations.

[0108] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit the present application. Although the present application has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present application.

Claims

1. A fluid-solid coupling numerical simulation method based on an embedded discrete fracture model, characterized in that: include: The reservoir matrix is ​​divided using structured grid technology to obtain a matrix grid, and the discrete fracture model is embedded into the matrix grid to obtain a geological grid model of the oil and gas reservoir; According to the fluid exchange mechanism between fractures and matrix, the transfer function between matrix and fractures is established; A porous medium fluid seepage control equation is established based on the transfer function between the matrix and the fracture; wherein the porous medium fluid seepage control equation includes a porous medium seepage control equation for the gas phase and the water phase in the matrix and a fracture seepage control equation for the gas phase and the water phase in the fracture; At each time point, combined with the reservoir geological grid model, the porous media fluid seepage control equation is solved to obtain the pore pressure field of the matrix and fractures in the formation; The weighted average of matrix pressure and fracture pressure is calculated by volume weighted average method to obtain equivalent pore pressure field, which is used as the boundary condition of solid mechanics control equation. Expand the geological grid model of oil and gas reservoirs, expand the overlying stratum grid, underlying stratum grid and lateral stratum grid, assign corresponding mechanical properties to the expanded stratum grid, and obtain the ground stress grid model; By using the flexibility superposition method to equate the mechanical properties of the fracture to the increase of the unit flexibility, a fracture-rock constitutive model is constructed. Combining the effective stress principle, the fracture-rock constitutive model and the stress equilibrium equation, the solid mechanics control equation is constructed. Finite element discretization method and Newton-Raphson method are used to iteratively solve the solid mechanics control equations to obtain strain, displacement and effective stress to simulate the deformation behavior of rocks during oil and gas production; Based on the constitutive relationship of the composite material, the strain of the matrix and the crack is calculated. Based on the strain of the matrix and the crack, the seepage properties of the crack and the matrix are calculated and updated for the seepage field calculation; Based on the iterative coupling method, the coupling effect between the seepage field and the stress field is considered; The method of using the flexibility superposition method to equate the mechanical properties of the fracture to the increase of the unit flexibility to construct a fracture-rock constitutive model includes: the expression of the fracture-rock constitutive model is: ;in, is the effective stress, is the dependent variable, is the flexibility matrix of the matrix material, which is used to describe the flexibility characteristics of crack-free rock. is the flexibility matrix of the fracture material, which combines the flexibility characteristics of the fracture and the influence of the anisotropic elastic modulus of the rock caused by the fracture. is the volume fraction of the matrix material, is the volume fraction of crack material, is the equivalent stiffness; The solid mechanics control equation is constructed by combining the effective stress principle, the fracture-rock constitutive model and the stress balance equation, including: the effective stress principle is: in a porous medium, the total stress is decomposed into two parts: effective stress and pore pressure; the stress balance equation describes the equilibrium state of stress inside the rock; the strain relationship equation links the strain variable with the displacement field; the expression of the solid mechanics control equation is: ;in, is the equivalent stiffness, is the spatial gradient, is the displacement field, is the expression of the dependent variable, is the biot coefficient, is the pore pressure, is the identity matrix, is the body density vector, is the transpose operation.

2. The fluid-solid coupling numerical simulation method based on the embedded discrete fracture model according to claim 1 is characterized in that: Also includes: Set the reservoir seepage parameters, set the reservoir initial conditions, and set the development strategy.

3. The fluid-solid coupling numerical simulation method based on the embedded discrete fracture model according to claim 1 is characterized in that: The method further includes: using the initial geostress field as an initial condition to initialize the static balance of the geostress field before calculating the weighted average of the matrix pressure and the fracture pressure by the volume weighted average method to obtain the equivalent pore pressure field and using the equivalent pore pressure field as the boundary condition of the solid mechanics control equation.

4. The fluid-solid coupling numerical simulation method based on the embedded discrete fracture model according to claim 3 is characterized in that: The initial geostress field is expressed by three stresses, namely vertical stress, minimum horizontal principal stress and maximum horizontal principal stress, and the direction of the minimum horizontal principal stress.

5. The fluid-solid coupling numerical simulation method based on an embedded discrete fracture model according to claim 3, characterized in that: The weighted average of the matrix pressure and the fracture pressure is calculated by the volume weighted average method to obtain the equivalent pore pressure field, including: According to the formula Calculate the weighted average of matrix pressure and fracture pressure to obtain the equivalent pore pressure field; where, is the equivalent pore pressure field, is the matrix pressure, is the crack pressure, For the entire computational domain, is the volume element, Represents volume Perform integration.

6. The fluid-solid coupling numerical simulation method based on an embedded discrete fracture model according to claim 1, characterized in that: The method of calculating the strain of the matrix and the crack based on the constitutive relationship of the composite material includes: According to the constitutive relation of composite materials, the matrix and crack are regarded as a whole, and its strain is the superposition of the strain of the matrix and crack; The constitutive relation and strain relation of the composite material are used to calculate the strains of the matrix and crack in three orthogonal directions respectively; wherein the strain relation is defined as the strain of the matrix and crack is the sum of the strains in the three orthogonal directions.

7. The fluid-solid coupling numerical simulation method based on an embedded discrete fracture model according to claim 1, characterized in that: The method of calculating and updating the seepage properties of the fractures and the matrix based on the strains of the matrix and the fractures comprises: The seepage properties of fractures include the normal strain of the fracture and the permeability of the fracture; The permeability properties of the matrix include the porosity of the matrix and the permeability of the matrix; According to the formula Calculate the normal strain of the crack; where, is the normal stress of the crack, is the initial normal stress of the crack, is the normal strain of the crack, is the normal flexibility coefficient of the crack; According to the formula Calculate the updated crack opening; where, is the updated opening of the crack, is the initial opening of the crack; According to the formula Calculate the permeability of the fracture; where, is the permeability of the fracture; According to the formula Calculate the porosity of the updated matrix; where, is the volume strain of the matrix, is the original porosity of the matrix, is the porosity of the updated matrix; According to the formula Calculate the permeability of the updated matrix; where, is the original permeability of the matrix, is the permeability of the updated matrix, is the empirical coefficient.

8. A fluid-solid coupling numerical simulation device based on an embedded discrete fracture model, characterized in that: include: Establishing an oil and gas reservoir geological grid module, which is used to divide the reservoir matrix using structured grid technology to obtain a matrix grid, embed the discrete fracture model into the matrix grid, and obtain an oil and gas reservoir geological grid model; Establishing a transfer function module for establishing a transfer function between the matrix and the fracture according to the fluid exchange mechanism between the fracture and the matrix; Establishing a control equation module for establishing a porous medium fluid seepage control equation based on a transfer function between the matrix and the fracture; wherein the porous medium fluid seepage control equation includes a porous medium seepage control equation for a gas phase and a water phase in the matrix and a fracture seepage control equation for a gas phase and a water phase in the fracture; The seepage control equation solving module is used to solve the porous medium fluid seepage control equation at each time node in combination with the oil and gas reservoir geological grid model to obtain the pore pressure field of the matrix and fractures in the formation; An equivalent pore pressure field acquisition module is used to calculate the weighted average of matrix pressure and fracture pressure by volume weighted average method to obtain the equivalent pore pressure field, and use the equivalent pore pressure field as the boundary condition of the solid mechanics control equation; Constructing a geostress grid model to expand the oil and gas reservoir geological grid model, expanding the overlying stratum grid, the underlying stratum grid and the lateral stratum grid, giving the expanded stratum grid corresponding mechanical properties, and obtaining a geostress grid model; Constructing a solid mechanics control equation module, which is used to construct a fracture-rock constitutive model by using the flexibility superposition method to equate the fracture mechanical properties to the increase in unit flexibility. Combining the effective stress principle, the fracture-rock constitutive model and the stress equilibrium equation, the solid mechanics control equation is constructed. Solid mechanics control equation solving module, which is used to iteratively solve the solid mechanics control equation using finite element discretization method and Newton-Raphson method to obtain strain, displacement and effective stress to simulate the deformation behavior of rock during oil and gas extraction; The seepage parameter update module is used to calculate the strain of the matrix and cracks based on the constitutive relationship of the composite material, calculate and update the seepage properties of the cracks and matrix based on the strain of the matrix and cracks, and use them for seepage field calculation; based on the iterative coupling method, the coupling effect between the seepage field and the stress field is considered; The method of using the flexibility superposition method to equate the mechanical properties of the fracture to the increase of the unit flexibility to construct a fracture-rock constitutive model includes: the expression of the fracture-rock constitutive model is: ;in, is the effective stress, is the dependent variable, is the flexibility matrix of the matrix material, which is used to describe the flexibility characteristics of crack-free rock. is the flexibility matrix of the fracture material, which combines the flexibility characteristics of the fracture and the influence of the anisotropic elastic modulus of the rock caused by the fracture. is the volume fraction of the matrix material, is the volume fraction of crack material, is the equivalent stiffness; The solid mechanics control equation is constructed by combining the effective stress principle, the fracture-rock constitutive model and the stress balance equation, including: the effective stress principle is: in a porous medium, the total stress is decomposed into two parts: effective stress and pore pressure; the stress balance equation describes the equilibrium state of stress inside the rock; the strain relationship equation links the strain variable with the displacement field; the expression of the solid mechanics control equation is: ;in, is the equivalent stiffness, is the spatial gradient, is the displacement field, is the expression of the dependent variable, is the biot coefficient, is the pore pressure, is the identity matrix, is the body density vector, is the transpose operation.

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