A method of simulating the flow of petroleum in the subsurface

Abstract

The application provides a method for simulating the flow state of oil in the ground, and belongs to the technical field of oil exploration, and comprises the following steps: when simulating the flow state of oil in the ground by using a color gradient lattice Boltzmann multiphase flow model: using a central difference method, grid variables of virtual adjacent grid points of an import and export boundary grid point f(i,j) of the color gradient lattice Boltzmann multiphase flow model are solved; using the grid variables of the virtual adjacent grid points of f(i,j), a fluid phase field gradient ∇ρ N and an interface curvature κ in a continuous surface force model of the color gradient lattice Boltzmann multiphase flow model are solved; wherein the fluid phase field gradient ∇ρ N are used for determining a fluid color gradient phase field, and the interface curvature κ is used for determining a two-phase interface tension. The method solves the problem that, when simulating the flow state of oil in the ground by using the color gradient lattice Boltzmann multiphase flow model, physical quantities at fluid grid points at import and export boundaries lack corresponding information in some calculation directions, so that the boundary grid points are distorted when calculated.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oil exploration, and particularly relates to a method for simulating the flow state of oil in the ground. BACKGROUND

[0002] In the field of oil exploration, it is necessary to master the flow mechanism of oil in the ground, and then to carry out oil exploitation according to the flow state.

[0003] The method for simulating the flow state of oil in the ground can be simulated by using the method for simulating the multiphase flow of porous media, wherein the lattice Boltzmann method is a common method for simulating the multiphase flow of porous media.

[0004] The lattice Boltzmann (LBM) method is derived from the lattice gas automata method, and is a discrete format for solving the continuous Boltzmann equation. The method can obtain the macroscopic quantities of the fluid, such as density, velocity and pressure, by solving the distribution function of the fluid particles. In addition, the lattice Boltzmann method can be reduced to the Navier-Stokes equation of the second order of accuracy through the Chapman-Enskog expansion analysis, and therefore can be considered as a special solver for solving the Navier-Stokes equation.

[0005] Compared with the traditional computational fluid dynamics methods such as the finite difference method, the finite element method and the finite volume method, the LBM method has significant advantages in program compilation, parallel computing, boundary processing and interface tracking operation.

[0006] In the LBM method, the popular method is the color gradient method, which can realize high viscosity ratio multiphase flow while maintaining high calculation accuracy and execution efficiency, and has been widely applied in the field of porous media fluid flow. In recent years, the development and improvement of the method mainly lies in the calculation and solving accuracy of the color gradient, the design of the perturbation step, the judgment of the two-phase interface and the wet boundary condition.

[0007] The current fluid color gradient phase field adopts the fourth-order isotropic difference calculation, and the two-phase interface tension is obtained by using the continuous surface force model.

[0008] However, the method has the problem that the physical quantities at the fluid grid points at the inlet and outlet boundaries of the calculation model lack corresponding information in some calculation directions, resulting in distortion of the calculation of the boundary grid points. SUMMARY

[0009] In order to overcome the defects of the prior art, the application provides a method for simulating the flow state of oil in the ground.

[0010] In order to achieve the above purpose, the application provides the following technical scheme:

[0011] A method for simulating the flow state of oil in the ground, comprising:

[0012] In simulating the flow state of oil in the ground by using a color gradient lattice Boltzmann multiphase flow model:

[0013] Using the central difference method, the grid variable of the virtual neighboring grid point of the inlet and outlet boundary grid point of the color gradient lattice Boltzmann multiphase flow model is solved;

[0014] Using the grid variable of the virtual neighboring grid point of the color gradient lattice Boltzmann multiphase flow model, the fluid phase field gradient and the interface curvature in the continuous surface force model formula of the color gradient lattice Boltzmann multiphase flow model are solved; wherein the fluid phase field gradient is used to determine the fluid color gradient phase field, and the interface curvature is used to determine the two-phase interfacial tension. Further, the grid variable of the virtual neighboring grid point of the color gradient lattice Boltzmann multiphase flow model is used to solve the fluid phase field gradient

[0015] and the interface curvature in the continuous surface force model formula of the color gradient lattice Boltzmann multiphase flow model, comprising: Substituting the grid variable of the virtual neighboring grid point of the color gradient lattice Boltzmann multiphase flow model into the difference formula of the color gradient lattice Boltzmann multiphase flow model, the fourth-order isotropic difference derivative of the color gradient lattice Boltzmann multiphase flow model is obtained.

[0016] Using the fourth-order isotropic difference derivative of the color gradient lattice Boltzmann multiphase flow model, the fluid phase field gradient and the interface curvature in the continuous surface force model formula of the color gradient lattice Boltzmann multiphase flow model are calculated. Further, the difference formula of the color gradient lattice Boltzmann multiphase flow model is:

[0017] In the formula, c is 1; the weight coefficient is

[0018] ; the vector is represented as ;

[0019] , which represents the surrounding 9 neighboring grid points including the boundary grid point itself. Further, the method further comprises:

[0020] , which represents the surrounding 9 neighboring grid points including the boundary grid point itself.

[0021] Further, the method further comprises:​​​​​​ The fourth-order isotropic difference derivative is:

[0022] ;

[0023] .

[0024] Furthermore, the formula for the continuous surface force model is:

[0025]

[0026] in, For surface force, For the interface curvature, For the fluid phase field gradient, For interface tension.

[0027] Furthermore, the fluid phase field gradient for:

[0028] ;

[0029] .

[0030] Furthermore, interface curvature for:

[0031] ;

[0032] ;

[0033] ;

[0034] .

[0035] The method for simulating the underground flow of oil provided by this invention has the following beneficial effects:

[0036] This invention utilizes a color gradient lattice Boltzmann multiphase flow model to simulate the flow state of oil underground and obtain the physical quantities of underground oil; it uses the central difference method to calculate the grid variables of neighboring grid points at the inlet and outlet boundary grid points of the color gradient lattice Boltzmann multiphase flow model, and utilizes... The color gradient lattice is obtained by calculating the mesh variables of the virtual neighboring lattice. The fluid phase field gradient in the continuous surface force model formula of the Boltzmann multiphase flow model is obtained. and interface curvature , and further obtain fluid color gradient phase field and two-phase interface tension; solve the problem that in the prior art, when simulating the flow state of underground oil by using the color gradient lattice Boltzmann multiphase flow model, physical quantities at the fluid lattice points at the inlet and outlet boundaries lack corresponding information in some calculation directions, so that the boundary lattice points are distorted when calculated. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present application and the design scheme thereof, the drawings required by the present embodiments will be briefly introduced as follows. The drawings in the following description are only partial embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0038] Figure 1 It is a fourth-order isotropic difference schematic diagram of the present application.

[0039] Figure 2 It is a schematic diagram of the inlet and outlet boundary processing method of the present application. DETAILED DESCRIPTION

[0040] In order to make those skilled in the art better understand the technical scheme of the present application and can be implemented, the present application will be described in detail below in combination with the drawings and specific embodiments. The following embodiments are only used to more clearly illustrate the technical scheme of the present application, and cannot limit the protection scope of the present application.

[0041] Embodiment:

[0042] The present application provides a method for simulating the flow state of oil underground, specifically as shown in the figure, comprising: Figure 1

[0043] When simulating the flow state of underground oil by using the color gradient lattice Boltzmann multiphase flow model:

[0044] Using the central difference method, the grid variables of the virtual adjacent lattice points of the inlet and outlet boundary lattice points of the color gradient lattice Boltzmann multiphase flow model are solved; using the grid variables of the virtual adjacent lattice points, the fluid phase field gradient and the interface curvature in the continuous surface force model of the color gradient lattice Boltzmann multiphase flow model are solved; wherein the fluid phase field gradient is used to determine the fluid color gradient phase field, and the interface curvature is used to determine the two-phase interface tension. The grid variables of the virtual adjacent lattice points of the inlet and outlet boundary lattice points are:

[0045] The grid variables of the virtual adjacent lattice points of the inlet and outlet boundary lattice points are:

[0046] ​​The mesh variables of the virtual neighboring grid points of the import boundary grid point:

[0047] (1)

[0048] The grid variables of the virtual neighboring grid points of the exit boundary grid point:

[0049] (2)

[0050] in, These are grid points representing import and export boundaries.

[0051] The following is a detailed explanation of the technical problem addressed by this invention:

[0052] In the color gradient model, the interface curvature in the continuous surface force model formula (3) and fluid phase field The gradient calculation requires the use of fourth-order isotropic difference, and the specific calculation process is shown in formulas (301) and (302).

[0053] (3)

[0054] (301)

[0055] (302)

[0056] in, For surface force, For the interface curvature, For the fluid phase field gradient, For interface tension.

[0057] The fourth-order isotropic difference scheme is as follows: Figure 1 As shown, when solving for the gradient at the central grid point, information from the surrounding grid points is required. This approach can greatly reduce the influence of the interface pseudopotential and improve computational stability.

[0058] With variables For example, its difference formula is expressed as follows:

[0059] (4)

[0060] In the formula, c is 1; weighting coefficient Represented as ;vector Represented as ; This represents the 9 neighboring grid points (including itself) around a grid point, such as... Figure 1 As shown, Represents the grid variable in the i-th row and j-th column;

[0061] However, in the treatment of the model import and export, respectively, lack of a row of grid information, such as Figure 2 The virtual boundary row as shown. With import boundary grid For example, the adjacent grid , And Are unknown, which makes formula (4) can not be effectively applied.

[0062] The following is the main technical solution of the invention:

[0063] The patent proposes to use a simple central difference method to solve the information of the virtual boundary column, for import and export boundary,

[0064] Import boundary: (1)

[0065] Export boundary: (2)

[0066] Substitute formula (1) and formula (2) into formula (4), the four-order isotropic difference derivative of the variable at the import and export boundary can be obtained explicitly.

[0067] Similarly, take the import boundary grid For example:

[0068] (5)

[0069] (6)

[0070] Generally in the lattice Boltzmann flow simulation, the top and bottom boundaries (or left and right boundaries) of the calculation region are generally set as solid grid points, and only the information of the fluid grid points is concerned in the calculation. Therefore, by formula (5) and (6), the difference results of each fluid grid point at the import and export boundary can be obtained.

[0071] The following is the implementation method of the invention:

[0072] In general, the color gradient lattice Boltzmann simulation method actually includes the following five steps in the program: 1. Calculation of macroscopic quantities; 2. Collision step; 3. Perturbation step; 4. Migration step; 5. Boundary condition.

[0073] The boundary grid point information processing method proposed by the patent only needs to be implemented in the calculation of the surface continuous force in the 3 perturbation step, and the other steps can be processed according to the original method. Specifically:

[0074] When calculating the phase field gradient At the import and export boundary grid points, take the import grid point (i,j) as an example:

[0075] (7)

[0076] (8)

[0077] In calculating the curvature of the boundary grid point, the normal vector x and y direction need to be solved by difference respectively:

[0078] (9)

[0079] (10)

[0080] (11)

[0081] (12).

[0082] The above-described embodiments are merely the best preferred specific embodiments of the present application. The protection scope of the present application is not limited to this, and any simple change or equivalent replacement of the technical solution within the technical range disclosed by the present application, which can be obviously obtained by those skilled in the art, shall belong to the protection scope of the present application.

Claims

1. A method for simulating the underground flow of oil, characterized in that, include: When simulating the flow state of underground oil using the color gradient lattice Boltzmann multiphase flow model: Using the central difference method, the inlet and outlet boundary lattice points of the color gradient lattice Boltzmann multiphase flow model are solved. The grid variable of virtual neighboring grid points; The mesh variables of the virtual neighboring grid points of the import boundary grid point: The grid variables of the virtual neighboring grid points of the exit boundary grid point: use Using the grid variables of virtual neighboring grid points, the fluid phase field gradient in the continuous surface force model of the Boltzmann multiphase flow model with color gradient lattice is obtained. and interface curvature Among them, the fluid phase field gradient Used to determine the phase field of fluid color gradient and interface curvature. Used to determine the interfacial tension between two phases; The use of The color gradient lattice is obtained by calculating the mesh variables of the virtual neighboring lattice. The fluid phase field gradient in the continuous surface force model formula of the Boltzmann multiphase flow model is also calculated. and interface curvature ,include: Will Substitute the grid variables of the virtual neighboring grid points From the difference formula, we get The fourth-order isotropic difference derivative; use The fluid phase field gradient in the formula for the continuous surface force model of the Boltzmann multiphase flow model for calculating the color gradient using the fourth-order isotropic differential derivative. and interface curvature .

2. The method for simulating the underground flow of oil according to claim 1, characterized in that, The difference formula is: In the formula, c is 1; weighting coefficient for ;vector Represented as ; , represents the nine neighboring grid points surrounding the boundary grid point itself.

3. The method for simulating the underground flow state of oil according to claim 1, characterized in that, The The fourth-order isotropic difference derivative is: ； 。 4. The method for simulating the underground flow of oil according to claim 1, characterized in that, The formula for the continuous surface force model is: in, For surface force, For the interface curvature, For the fluid phase field gradient, For interface tension.

5. The method for simulating the underground flow state of oil according to claim 1, characterized in that, Fluid phase field gradient for: ； 。 6. The method for simulating the underground flow state of oil according to claim 1, characterized in that, Interface curvature for: ； ； ； 。

Images