Reservoir rock permeability prediction method and device based on fracture network model

Abstract

The present invention discloses a reservoir rock permeability prediction method and device based on a fracture network model, the method comprising: establishing a flow calculation model for an elliptical cross-section pipeline under the action of a pulsating wave: for the established three-dimensional fracture network model, determining the flow calculation equations at both ends of each pipeline in the three-dimensional fracture network model according to the flow calculation model; listing the flow conservation equations for the flow calculation equations at both ends of the pipeline of each node in the three-dimensional fracture network model to obtain the flow linear equation group of each node; determining the inlet pressure and outlet pressure of each pipeline according to the flow linear equation group of each node; substituting the inlet pressure and outlet pressure of each node into the flow calculation equation to determine the flow at both ends of each pipeline; determining the permeability of the three-dimensional fracture network model according to the flow at both ends of each pipeline and the pipeline information. The present invention can conduct a more in-depth study on the reservoir rock problem containing fractures and pores.

Description

Technical Field

[0001] The invention relates to the technical field of seismic wave exploration of complex oil and gas reservoirs, and in particular to a method and device for predicting reservoir rock permeability based on a fracture network model. Background Art

[0002] This section is intended to provide a background or context to the embodiments of the invention recited in the claims. No admission is made that the description herein is prior art by inclusion in this section.

[0003] In the seismic exploration of complex oil and gas reservoirs, it is inevitable to encounter the problem of reservoir rocks containing fractures and pores. The pore structure of these rocks is complex and the properties of pore fluids are variable, which leads to the dispersion and attenuation of seismic wave field signals. At the same time, establishing a reasonable fluid-containing pore-fracture rock physics model is also a necessary basis for seismic wave forward modeling, reservoir fluid prediction and other technologies. The commonly used fracture-pore medium models are as follows.

[0004] ①. Method of establishing a pore elastic medium model from a microscopic scale. This method is to establish a regular cubic grid at a microscopic scale. Each grid point has flow channels in six directions: up, down, left, right, front and back. The model assumes that the fluid flow between the grid point and other adjacent nodes satisfies Darcy's law. When the porous space unit represents a crack, the author assumes that the crack direction is randomly distributed in space. By introducing the volume ratio of cracks and pores, the proportional relationship parameters between cracks and pores are obtained. After obtaining the average expected value of the pressure at the grid node, based on the assumption that the grid points are uniform, the model uses the method of summing and averaging at multiple nodes to obtain Darcy's law at a macroscopic scale. The model adopts the long wavelength assumption and obtains the wave equation by Taylor expansion of the pressure near the grid point. The model introduces permeability at a microscopic scale, but does not establish a relationship between permeability and influencing factors such as crack parameters and confining pressure, nor does it give an expression for the permeability of porous media. The model mentions permeability as a calculation parameter, which needs to be measured by experimental means.

[0005] ② A linear sliding model is proposed for a dry skeleton with horizontal cracks. This model represents the constitutive relationship of the porous medium with cracks inside the unit body V as a flexible correction form for the background medium. This model is a macro model and is applicable to media containing multiple layers of horizontal cracks. However, the disadvantage of this model is that it does not consider pores and fluids, lacks the microstructural characteristics of cracks, and therefore cannot predict the effect of cracks on permeability.

[0006] ③. Horizontal layered fracture anisotropy model. Under the long wavelength assumption, parallel fractures are embedded in the isotropic medium. The model takes into account the complex stiffness coefficients in the normal and tangential directions of the fractures, and obtains the anisotropic characteristics of P and S wave attenuation. This model is a macroscopic model that takes into account horizontal layered fractures, but lacks the microstructural characteristics of the fractures and does not model the permeability of the fracture system.

[0007] ④. Wave equation model for porous media with fractures. Starting from the constitutive relationship between solid and fluid, this model considers the fractures randomly distributed in three-dimensional space, introduces the jet flow effect between the fractures and adjacent pores, and obtains the wave equation considering the fracture effect. In the derivation process, this model cited the dynamic permeability model proposed by other scholars, but did not give the relationship between permeability and fractures.

[0008] In summary, the existing major fractured porous media models do not provide a method for characterizing permeability, and it is impossible to establish a direct relationship between microscopic fracture parameters and macroscopic permeability, resulting in an inability to conduct more in-depth research on reservoir rock problems containing fractures and pores. Summary of the invention

[0009] The embodiment of the present invention provides a reservoir rock permeability prediction method based on a fracture network model, which is used to establish a direct relationship between microscopic fracture parameters and macroscopic permeability, so as to conduct a more in-depth study on reservoir rock problems containing fractures and pores. The method includes:

[0010] According to the pipeline information of the elliptical cross-section pipeline and the fluid information in the pipeline, a flow calculation model of the elliptical cross-section pipeline under the action of pulsating waves is established, and the flow calculation model includes flow calculation models at the pipeline inlet and outlet:

[0011] For the established three-dimensional fracture network model, determining the flow calculation equations at both ends of each pipeline in the three-dimensional fracture network model according to the flow calculation model;

[0012] The flow conservation equations are formulated for the flow calculation equations at both ends of the pipelines at each node in the three-dimensional fracture network model to obtain a flow linear equation group for each node, wherein the node is an intersection point of multiple pipelines;

[0013] Determine the inlet and outlet pressures of each pipeline according to the linear flow equations of each node;

[0014] Substitute the inlet and outlet pressures of each pipeline into the flow calculation equation to determine the flow at both ends of each pipeline;

[0015] The permeability of the three-dimensional fracture network model is determined according to the flow rates at both ends of each pipeline and the pipeline information.

[0016] The embodiment of the present invention further provides a reservoir rock permeability prediction device based on a fracture network model, the device comprising:

[0017] The model building module is used to establish a flow calculation model of the elliptical cross-section pipeline under the action of pulsating waves according to the pipeline information of the elliptical cross-section pipeline and the fluid information in the pipeline. The flow calculation model includes flow calculation models at the pipeline inlet and outlet:

[0018] A calculation module, for determining the flow calculation equations at both ends of each pipeline in the three-dimensional fracture network model according to the flow calculation model for the established three-dimensional fracture network model;

[0019] The calculation module is also used to formulate flow conservation equations for the flow calculation equations at both ends of the pipelines at each node in the three-dimensional fracture network model to obtain a flow linear equation group for each node, wherein the node is an intersection of multiple pipelines;

[0020] The calculation module is also used to determine the inlet pressure and the outlet pressure of each pipeline according to the flow linear equation group of each node;

[0021] The calculation module is also used to substitute the inlet pressure and the outlet pressure of each pipeline into the flow calculation equation to determine the flow at both ends of each pipeline;

[0022] The calculation module is also used to determine the permeability of the three-dimensional fracture network model according to the flow at both ends of each pipeline and the pipeline information.

[0023] An embodiment of the present invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the above-mentioned reservoir rock permeability prediction method based on the fracture network model when executing the computer program.

[0024] An embodiment of the present invention also provides a computer-readable storage medium, which stores a computer program for executing the above-mentioned reservoir rock permeability prediction method based on the fracture network model.

[0025] In the embodiment of the present invention, for the problem of seismic wave velocity dispersion and attenuation prediction in porous media containing cracks, a three-dimensional fracture network model is established considering the influence of the three-dimensional fracture network on the fluid permeability, and by establishing a flow calculation model for an elliptical cross-section pipeline, a flow conservation equation for the flow calculation equation at both ends of the pipeline at each node is established, so that the model is closer to the real situation; then, the flow conservation equation is solved to obtain the inlet pressure and outlet pressure of each pipeline, thereby obtaining the flow at the inlet and outlet of each pipeline, and the permeability calculation method of the three-dimensional fracture network model is determined in combination with the flow and pipeline information, and a direct relationship is established between the microscopic fracture parameters and the macroscopic permeability, so as to conduct a more in-depth study on the reservoir rock problem containing cracks and pores. In addition, actual data analysis shows that the embodiment of the present invention realizes the accurate characterization of the internal flow characteristics of fluids in porous rocks containing cracks, which has obvious advantages over traditional methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0027] Figure 1 It is a flow chart of a reservoir rock permeability prediction method based on a fracture network model in an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of radial coordinates of an elliptical cylindrical coordinate system in an embodiment of the present invention;

[0029] Figure 3 is a schematic diagram of an elliptical coordinate system in an embodiment of the present invention;

[0030] Figure 4 is a schematic diagram of a porous medium containing a three-dimensional fracture network in an embodiment of the present invention;

[0031] Figure 5 A schematic diagram of fluid flow conservation at a node in a three-dimensional fracture network according to an embodiment of the present invention;

[0032] Figure 6 A dynamic permeability prediction curve diagram of a water-containing fracture network porous medium in an embodiment of the present invention;

[0033] Figure 7 A prediction curve diagram of the dynamic permeability of a water-containing fracture network porous medium as a function of the fracture aspect ratio in an embodiment of the present invention;

[0034] Figure 8 This is a schematic diagram of the permeability change of a three-dimensional water-bearing fracture network (elliptical cross section) in sandstone in an embodiment of the present invention;

[0035] Fig. 9 This is a schematic diagram of the permeability change of a three-dimensional water-bearing fracture network (elliptical cross section) in dolomite in an embodiment of the present invention;

[0036] Fig.10 This is a schematic diagram of the permeability change of a three-dimensional water-bearing fracture network (elliptical cross section) in mudstone in an embodiment of the present invention;

[0037] Fig.11 It is a structural schematic diagram of a reservoir rock permeability prediction device based on a fracture network model in an embodiment of the present invention;

[0038] Fig.12 The figure is a schematic diagram of the structure of a computer device in an embodiment of the present invention. DETAILED DESCRIPTION

[0039] To make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. Here, the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0040] The embodiment of the present invention provides a reservoir rock permeability prediction method based on a fracture network model, such as Figure 1 As shown, the method includes steps 101 to 106:

[0041] Step 101: According to the pipeline information of the elliptical cross-section pipeline and the fluid information in the pipeline, a flow calculation model of the elliptical cross-section pipeline under the action of pulsating waves is established, and the flow calculation model includes flow calculation models at the pipeline inlet and outlet.

[0042] The pipeline information of the elliptical cross-section pipeline includes the major axis radius R1, the minor axis radius R2 and the pipeline length L of the elliptical cross-section pipeline; the fluid information includes the density ρ of the fluid in the pipeline f , the viscosity η of the fluid in the pipe and the speed c of the sound wave in the fluid. Here c is a complex number.

[0043] According to the pipeline information of the elliptical cross-section pipeline and the fluid information in the pipeline, the flow calculation model of the elliptical cross-section pipeline under the action of pulsating waves is established as follows:

[0044]

[0045] Among them, Q Ue , Q De They represent the flow rate at the inlet and outlet of the elliptical cross-section pipe under the action of pulsating waves; a represents the aspect ratio, i represents an imaginary number; P U , P D Respectively represent the pressure at the inlet and outlet of the pipeline; ω represents the frequency; J1(·) represents the first-order Bessel function; J0(·) represents the zero-order Bessel function; R represents the radius of the circular pipeline approximated by the elliptical pipeline; K represents the independent variable coefficient of the Bessel function, λ represents a dimensionless frequency parameter.

[0046] Step 102: for the established three-dimensional fracture network model, determine the flow calculation equations at both ends of each pipeline in the three-dimensional fracture network model according to the flow calculation model.

[0047] See also Figure 4 , is a schematic diagram of a porous medium containing a three-dimensional fracture network. Figure 3 As can be seen in the figure, the three-dimensional fracture network model contains many crisscross fractures, which can be regarded as pipes for fluid circulation. Cracks are generally approximately elliptical. In the three-dimensional fracture network model established in the embodiment of the present invention, an ellipse is used as the fracture shape, and the flow calculation model of the elliptical cross-section pipe is used to determine the flow calculation equations at both ends of each pipe in the three-dimensional fracture network model.

[0048] Step 103: The flow calculation equations at both ends of the pipeline of each node in the three-dimensional fracture network model are sequenced into flow conservation equations to obtain a flow linear equation group of each node, where the node is the intersection of multiple pipelines.

[0049] The three-dimensional fracture network model contains multiple pipes, and the intersections of multiple pipes are used as nodes. Figure 5 , which is a schematic diagram of fluid flow conservation at a three-dimensional fracture network node. The figure shows a node, which is the intersection of six pipelines.

[0050] For each node, the flow satisfies Kirchoff's law, that is, the flow into the node is equal to the flow out of the node, with the inflow flow as positive and the outflow flow as negative, then the sum of the inflow flow and the outflow flow is equal to 0, that is, Figure 5 As shown in , I1+I2+I3+(-I4)+(-I5)+(-I6)=0.

[0051] Step 104: Determine the inlet pressure and outlet pressure of each pipeline according to the flow linear equation group of each node.

[0052] In each flow calculation equation, the inlet pressure and outlet pressure are unknown quantities. Solving the flow linear equation group of each node can determine the inlet pressure and outlet pressure of each pipe constituting the node.

[0053] Step 105: Substitute the inlet pressure and outlet pressure of each pipeline into the flow calculation equation to determine the flow at both ends of each pipeline.

[0054] Step 106: Determine the permeability of the three-dimensional fracture network model according to the flow rates at both ends of each pipeline and the pipeline information.

[0055] Specifically, the total length of all pipes at the outlet end of the three-dimensional network model connected to the outside world and the sum of the cross-sectional areas of the elliptical cross-sections of each pipe are calculated; the sum of the outlet flow rates of the three-dimensional fracture network model connected to the outside world is calculated according to the flow rates at both ends of each pipe; the permeability of the three-dimensional fracture network model is determined according to the sum of the outlet flow rates, the total length, the sum of the cross-sectional areas, the inlet pressure of the fluid injected into the three-dimensional fracture network model, and the outlet pressure connected to the outside world.

[0056] In the embodiment of the present invention, see Figure 4 Each face of the cube contains 9 pipes, which are the pipes connecting to the outside world. Figure 4 The side pointed by the middle arrow is the inlet end for injecting fluid, that is, there are 9 pipes at the inlet end. Generally, when conducting a permeability test, one side is reserved for injecting fluid, the other side is reserved for leaking fluid, and the other sides are blocked. The 9 pipes on the side for leaking fluid are used as all the pipes at the outlet end connected to the outside world.

[0057] The permeability of the three-dimensional fracture network model is determined according to the following formula:

[0058]

[0059] Where κ(ω) represents the permeability of the three-dimensional fracture network model when the frequency is ω; ∑Q De represents the total flow rate at the outlet of the three-dimensional fracture network model connected to the outside world; ∑A represents the sum of the cross-sectional areas of the elliptical cross sections of each pipe at the outlet of the three-dimensional network model connected to the outside world, where the cross-sectional area of ​​each pipe is A = aπR1 2 ; ∑L represents the total length of all pipes at the outlet of the three-dimensional network model connected to the outside world; P D ' represents the inlet pressure of the injected fluid in the three-dimensional fracture network model; P U ' represents the outlet pressure of the three-dimensional fracture network model connected to the outside world.

[0060] It should be noted that P D 'Determined by the experimenter; since the outlet is connected to the outside, in the outside atmosphere, P U ' is the atmospheric pressure value.

[0061] It should be noted that the above method proposed in the embodiment of the present invention considers that:

[0062] (1) The permeability of fluid flow in the porous medium of the fracture network varies with frequency, and different frequencies correspond to different permeability values;

[0063] (2) For the fracture-pore network structure, the fracture parameters (volume density, aspect ratio, etc.) have a greater impact on the permeability-frequency relationship;

[0064] (3) The permeability of porous media containing fracture networks is a function of the fracture aspect ratio. Under given porosity and fracture density conditions, the permeability decreases rapidly as the fracture aspect ratio decreases.

[0065] That is to say, the permeability calculated by the embodiment of the present invention is a dynamic permeability, and the permeability calculated is different under different frequencies and different fracture parameters.

[0066] The process of establishing the flow calculation model of the elliptical cross-section pipeline under the action of pulsating waves in step 101 will be described in detail below.

[0067] In principle, the present invention introduces a pressure distribution that varies with frequency and spatial position in a single-tube flow based on a micro-tube flow model with an elliptical interface, thus overcoming the difficulty in calculating the velocity and flow rate in a dynamic flow field. By using the condition that the dimensionless flow rate in an elliptical interface pipe is independent of the aspect ratio, the problem of calculating the flow rate in an elliptical interface pipe is converted into the problem of calculating the flow rate in a circular interface pipe.

[0068] In the embodiment of the present invention, an elliptical cylindrical coordinate system is used for derivation, such as Figure 2 As shown, ξ and ψ represent the radial coordinates of the elliptical cylinder, and z represents the axial coordinates of the elliptical cylinder. According to the symmetry of the pipeline, the radial and axial velocities of the fluid flowing in the pipeline are independent of the angle. The radial and axial velocities of the fluid particle u=u(r,z,t), the radial velocity v=v(r,z,t), the fluid pressure p=p(r,z,t), the frequency is ω, and the density and viscosity of the fluid in the pipeline are ρ respectively. f , η, and assume that: the pipe is infinitely long, the pipe wall is rigid, and the pipe cross section is elliptical. Then the velocity field of the fluid in the elliptical cross section pipe satisfies:

[0069]

[0070] Among them, at low speed, the compressibility of the pore fluid can be ignored under the action of elastic waves, that is, Considering that the only non-zero velocity component is along the z-axis (axial direction), and the velocity depends only on the radial coordinate, we have v f T ={0,0,v fz}, so we get here is the material derivative of the fluid velocity field with respect to time. f represents the fluid velocity vector, v fz Represents the component of fluid velocity in the z direction.

[0071] Assuming that the axial velocity of the fluid along the cylinder under the action of pulsating pressure is u1, the fluid velocity field control equation is:

[0072]

[0073]

[0074] in is the compression factor.

[0075] See also Figure 3 , the elliptic cylindrical coordinate system and the Cartesian coordinate system satisfy:

[0076] x=dcoshξcosψ

[0077] y=dsinhξsinψ (4)

[0078] Among them, the distance between the two foci of the elliptical section is 2d, ψ=ψ0 represents a family of confocal hyperbolas, ξ=ξ0 represents a family of confocal ellipses, where ξ0 and ψ0 are constants. Using the coordinate transformation relationship, the Navier-Stokes equation in the elliptical cylindrical coordinate system is obtained:

[0079]

[0080] Considering the no-slip boundary condition on the elliptical pipe surface and the symmetry of the velocity field about the radius of the elliptical section, we get

[0081] u1(ξ0,ψ)=0 (6)

[0082]

[0083] Assume u1,p has the following variable separation form:

[0084]

[0085] Substituting into the Navier-Stokes equation we get:

[0086]

[0087] The above equation is a non-homogeneous differential equation about U. Under steady-state conditions, the spatial distribution of the velocity field is:

[0088]

[0089] In Cartesian coordinate system it is expressed as:

[0090]

[0091] Where R1 and R2 are the long and short radii of the ellipsoidal cross section. From the above formula, it can be seen that the maximum velocity on the cross section is Introducing the characteristic length describing the elliptical cross section The flow rate for steady-state flow can be easily obtained by integrating over the cross section:

[0092]

[0093] The flow rate in the Cartesian coordinate system is expressed as:

[0094]

[0095] Under non-steady-state conditions, define a dimensionless frequency parameter The Reynolds number Characteristic frequency The average velocity of the flow field is After simplification, we get It is easy to see that The dynamic component of the flow field velocity is expressed as Substitute the Navier-Stokes equation in the elliptic cylindrical coordinate system to obtain the homogeneous equation:

[0096]

[0097] If the speed U * It can be written in the form of separated variables U * (ξ,ψ)=f(ξ)g(ψ), after substituting into the above formula, we can get the dynamic component of the velocity field:

[0098]

[0099] where c e2n and C e2n denote the Mathieu function and the deformed Mathieu function respectively, coefficient It can be obtained through the recursive relationship between the function order 2n and the parameter q. Integrate the flow field velocity u1 inside the area D surrounded by the elliptical boundary to obtain the pipeline flow rate:

[0100]

[0101] Since the velocity field and flow rate formula of the fluid in the elliptical cross-section single tube contain Mathieu function, its accurate numerical calculation is difficult. Therefore, approximate conditions are used to achieve fast calculation of velocity field and flow rate. For a circular cross section, a = 1. When the aspect ratio a = 1, the flow rate Q of the elliptical cross section pipe flow e The flow rate Q degenerated to the circular cross-section pipe flow c ,

[0102]

[0103] where J0(·), J1(·) are zero-order and first-order Bessel functions, R is the radius of the circular pipe approximated by the ellipse. Studies have found that the dimensionless flow rate Q / Q0 in an elliptical cross-section pipe is independent of the aspect ratio [Haslam and Zamir, 1998], where Q0 is the flow rate of steady-state flow. Therefore, we can get

[0104]

[0105] In the above formula, Q e Indicates the flow rate of the elliptical cross-section pipe, Q c Indicates the flow rate of a circular cross-section pipe, Q 0e is the steady-state flow rate of the elliptical cross-section pipe, Considering the aspect ratio The steady-state flow can be further expressed as Let a = 1, and we can get the steady-state flow rate of a circular cross-section pipe. Here R1=R2=R. Therefore, it is easy to get Therefore, the flow rate of the elliptical cross-section pipe is

[0106]

[0107] Here Q c (t) is the flow rate of a circular cross-section pipe. Consider the pipe length to be L, and the pressures at both ends of the pipe to be P U , P D At this time, the pressure in the pipe is the superposition of two waves propagating in opposite directions, and the flow rates are Q U , Q D , at this time the pressure in the tube is the superposition of two waves propagating in opposite directions:

[0108] p(z,t)=B + e -iω(t-z / c) +B - e -iω(t+z / c) (twenty one)

[0109] To satisfy the boundary condition, that is, p(0,0)=P U , p(L,0)=P D ,get

[0110]

[0111] Similarly, the total flow rate in the pipe is expressed as

[0112] q(z,t)=Q + e -iω(t-z / c) +Q - e -iω(t+z / c) (twenty three)

[0113] To meet the initial boundary conditions, the flow formula at both ends of the pipeline is as follows:

[0114]

[0115] Therefore, the flow rate of the elliptical cross-section pipe under the action of pulsating waves is obtained:

[0116]

[0117] The above is the derivation process of the flow calculation model for elliptical cross-section pipes under the action of pulsating waves.

[0118] In the embodiment of the present invention, for the problem of seismic wave velocity dispersion and attenuation prediction in porous media containing cracks, a three-dimensional fracture network model is established considering the influence of the three-dimensional fracture network on the fluid permeability, and by establishing a flow calculation model for an elliptical cross-section pipeline, a flow conservation equation for the flow calculation equation at both ends of the pipeline at each node is established, so that the model is closer to the real situation; then, the flow conservation equation is solved to obtain the inlet pressure and outlet pressure of each pipeline, thereby obtaining the flow at the inlet and outlet of each pipeline, and the permeability calculation method of the three-dimensional fracture network model is determined in combination with the flow and pipeline information, and a direct relationship is established between the microscopic fracture parameters and the macroscopic permeability, so as to conduct a more in-depth study on the reservoir rock problem containing cracks and pores. In addition, actual data analysis shows that the embodiment of the present invention realizes the accurate characterization of the internal flow characteristics of fluids in porous rocks containing cracks, which has obvious advantages over traditional methods.

[0119] The embodiment of the present invention also provides two calculation examples using the above method, as shown below.

[0120] Example 1 Prediction of permeability of three-dimensional network porous media

[0121] The permeability prediction of the porous medium of the three-dimensional fracture network filled with water is investigated. For simplicity, the porous medium considered is composed of elliptical cylindrical pipes with the same length and radius, and the overall shape is a cube, and the side length is recorded as S. The number of grids m, n, and l along the three directions of the spatial coordinate axis is equal, then S = (m-1) L. The calculation method of the permeability is as mentioned above. The flow rate of each node satisfies Kirchoff's law. The flow rate in each pipeline is calculated using the flow calculation model of the present invention, and a linear equation group can be obtained. The unknown quantity is the pressure of the pipeline at each node. Solving this equation group can calculate the flow rate of the porous medium of the three-dimensional pipeline network and then calculate the permeability.

[0122] Regarding the boundary conditions, a constant pressure is applied along the direction of fluid flow (assuming the left boundary as the inlet and the right boundary as the outlet), and the pressures at both ends are 10 6 Pa, 10 5 Pa, the upper, lower, front and rear boundaries are closed, that is, the fluid will not flow out from these four boundaries. Here water is taken as the viscous fluid, and the fluid parameters are shown in Table 1 below:

[0123] Table 1

[0124]

[0125] First, consider the following three-dimensional fracture network parameters: the grid size is 5×5×5, the porosity φ is set to 0.05, and the cube side length S is set to 1 cm. The microscopic scale and radius of the fracture are related to the aspect ratio. When the aspect ratio is 1, the length of each pore microtube is 2.5 mm, and the radius of each pore microtube can be calculated to be about 0.15 mm. The permeability of the porous medium in the water-containing three-dimensional fracture network varies with frequency. Figure 6 As shown. It can be found

[0126] (1) In the low-frequency range (<10 Hz), the permeability values ​​of Newtonian fluids tend to be horizontal, indicating that the flow of fluid in the pores is steady at this time.

[0127] (2) When the frequency exceeds a certain range, the curves change in different forms. The permeability curve of the porous medium shows a downward trend, and the permeability decreases with increasing frequency, indicating that the permeability value changes dynamically with frequency.

[0128] The inventors further studied the effect of fracture aspect ratio on permeability. Figure 6 In the figure, it can be easily found that when the aspect ratio decreases from 1 to 0.4, the permeability curve becomes lower. In order to exclude the influence of porosity change, the porosity is 0.05. Different aspect ratios are selected for "fractures", from 0.1 to 1.0, with an interval of 0.1. Then, the variation curve between permeability and aspect ratio is calculated.

[0129] from Figure 7 Found in:

[0130] (1) As the crack aspect ratio decreases from 1 to 0, the permeability decreases. This is a reasonable fact because the cracks tend to close as the aspect ratio decreases.

[0131] (2) Frequency controls the decay pattern of permeability. Even in fractures of the same porosity, the permeability-aspect ratio relationship is very different at different frequencies. At very low frequencies (about 10 Hz or lower), the permeability-aspect ratio curve appears to be a downward parabola, while the curve appears linear at high frequencies. We also found that at extremely high frequencies, the permeability curves tend to overlap.

[0132] Example 2 Prediction of permeability of reservoir rocks with different mineral compositions

[0133] In order to verify the applicability of the present invention, permeability prediction calculations were performed on model samples with different mineral compositions.

[0134] Assume that there is a three-dimensional spatial fracture network evenly distributed in the porous medium, the porosity φ is set to 0.05, and the fluid in the porous medium is water. c When the crack cross-section aspect ratio is acting, it can be expressed as a function of the confining pressure [Berg Charles, 2012] where ν, E are the Poisson's ratio and Young's modulus of the solid skeleton mineral material, and the confining pressure p is obtained. c The crack flow rate under the action of in is the pore fluid pressure gradient. The fracture density is determined by the following method: there is a 5×5×5 fracture network inside a cube with a side length S of 1 cm. The confining pressure of the porous medium is set to 50 atmospheres (about 5 MPa). The mineral composition parameters are shown in Table 2 below:

[0135] Table 2

[0136]

[0137] Using the reservoir rock permeability prediction technology based on the fracture network model, we have studied the frequency variation function of porous media permeability under different fracture aspect ratios. This invention technology can give the permeability changes of sandstone, dolomite and mudstone containing fracture networks in the range of 10-50Hz ( Figure 8 , Fig. 9 , Fig.10 ). We found that:

[0138] (1) In the frequency range of 10-50 Hz, the permeability of sandstone gradually decreases as the frequency increases;

[0139] (2) Under given porosity, the permeability of circular porous media with an aspect ratio of 1 is the highest, and the permeability gradually decreases as the aspect ratio decreases;

[0140] (3) Under given porosity and fracture network density, the permeability of dolomite and mudstone varies with frequency and fracture aspect ratio in the same way as that of sandstone.

[0141] The present invention also provides a reservoir rock permeability prediction device based on a fracture network model, as described in the following embodiments. Since the principle of solving the problem by the device is similar to that of the reservoir rock permeability prediction method based on a fracture network model, the implementation of the device can refer to the implementation of the reservoir rock permeability prediction method based on a fracture network model, and the repeated parts will not be repeated.

[0142] like Fig.11 As shown, the device 1100 includes a model building module 1101 and a calculation module 1102 .

[0143] The model building module 1101 is used to build a flow calculation model of the elliptical cross-section pipeline under the action of pulsating waves according to the pipeline information of the elliptical cross-section pipeline and the fluid information in the pipeline. The flow calculation model includes flow calculation models at the inlet and outlet of the pipeline:

[0144] A calculation module 1102 is used to determine the flow calculation equations at both ends of each pipeline in the three-dimensional fracture network model according to the flow calculation model for the established three-dimensional fracture network model;

[0145] The calculation module 1102 is also used to formulate a flow conservation equation for the flow calculation equations at both ends of the pipeline at each node in the three-dimensional fracture network model to obtain a flow linear equation group at each node, where the node is the intersection of multiple pipelines;

[0146] The calculation module 1102 is also used to determine the inlet pressure and the outlet pressure of each pipeline according to the flow linear equation group of each node;

[0147] The calculation module 1102 is also used to substitute the inlet pressure and the outlet pressure of each pipeline into the flow calculation equation to determine the flow at both ends of each pipeline;

[0148] The calculation module 1102 is also used to determine the permeability of the three-dimensional fracture network model according to the flow at both ends of each pipeline and the pipeline information.

[0149] In one implementation of the embodiment of the present invention, the pipeline information of the elliptical cross-section pipeline includes the major axis radius R1, the minor axis radius R2 and the pipeline length L of the elliptical cross-section pipeline; the fluid information includes the density ρ of the fluid in the pipeline f , the viscosity η of the fluid in the pipe and the speed c of the sound waves in the fluid.

[0150] In one implementation of the embodiment of the present invention, the module establishment module 1101 establishes a flow calculation model of the elliptical cross-section pipeline under the action of a pulsating wave according to the pipeline information of the elliptical cross-section pipeline and the fluid information in the pipeline, as shown below:

[0151]

[0152] Among them, Q Ue , Q De They represent the flow rate at the inlet and outlet of the elliptical cross-section pipe under the action of pulsating waves; a represents the aspect ratio, i represents an imaginary number; P U , P D Respectively represent the pressure at the inlet and outlet of the pipeline; ω represents the frequency; J1(·) represents the first-order Bessel function; J0(·) represents the zero-order Bessel function; R represents the radius of the circular pipeline approximated by the elliptical pipeline; K represents the independent variable coefficient of the Bessel function, λ represents a dimensionless frequency parameter.

[0153] In one implementation of the embodiment of the present invention, the calculation module 1102 is used to:

[0154] Calculate the total length of all pipes at the outlet of the three-dimensional network model connecting to the outside world, as well as the sum of the cross-sectional areas of the elliptical cross sections of each pipe;

[0155] The total flow rate at the outlet of the three-dimensional fracture network model connected to the outside world is calculated according to the flow rate at both ends of each pipeline;

[0156] The permeability of the three-dimensional fracture network model is determined according to the total outlet flow, total length, total cross-sectional area, inlet pressure of the injected fluid of the three-dimensional fracture network model, and outlet pressure connected to the outside.

[0157] In one implementation of the embodiment of the present invention, the calculation module 1102 is used to:

[0158] according to Determine the permeability of a three-dimensional fracture network model;

[0159] Where κ(ω) represents the permeability of the three-dimensional fracture network model when the frequency is ω; ∑Q De represents the total flow rate at the outlet of the three-dimensional fracture network model connected to the outside world; ∑A represents the sum of the cross-sectional areas of the elliptical cross sections of each pipe at the outlet of the three-dimensional network model connected to the outside world, where the cross-sectional area of ​​each pipe is A = aπR1 2 ; ∑L represents the total length of all pipes at the outlet of the three-dimensional network model connected to the outside world; P D ' represents the inlet pressure of the injected fluid in the three-dimensional fracture network model; P U' represents the outlet pressure of the three-dimensional fracture network model connected to the outside world.

[0160] In the embodiment of the present invention, for the problem of seismic wave velocity dispersion and attenuation prediction in porous media containing cracks, a three-dimensional fracture network model is established considering the influence of the three-dimensional fracture network on the fluid permeability, and by establishing a flow calculation model for an elliptical cross-section pipeline, a flow conservation equation for the flow calculation equation at both ends of the pipeline at each node is established, so that the model is closer to the real situation; then, the flow conservation equation is solved to obtain the inlet pressure and outlet pressure of each pipeline, thereby obtaining the flow at the inlet and outlet of each pipeline, and the permeability calculation method of the three-dimensional fracture network model is determined in combination with the flow and pipeline information, and a direct relationship is established between the microscopic fracture parameters and the macroscopic permeability, so as to conduct a more in-depth study on the reservoir rock problem containing cracks and pores. In addition, actual data analysis shows that the embodiment of the present invention realizes the accurate characterization of the internal flow characteristics of fluids in porous rocks containing cracks, which has obvious advantages over traditional methods.

[0161] An embodiment of the present invention further provides a computer device, Fig.12 Schematic diagram of a computer device in an embodiment of the present invention. The computer device can implement all steps in the reservoir rock permeability prediction method based on the fracture network model in the above embodiment. The computer device specifically includes the following contents:

[0162] Processor (processor) 1201, memory (memory) 1202, communication interface (CommunicationsInterface) 1203 and communication bus 1204;

[0163] The processor 1201, the memory 1202, and the communication interface 1203 communicate with each other through the communication bus 1204; the communication interface 1203 is used to realize information transmission between related devices;

[0164] The processor 1201 is used to call the computer program in the memory 1202, and when the processor executes the computer program, the reservoir rock permeability prediction method based on the fracture network model in the above embodiment is implemented.

[0165] An embodiment of the present invention also provides a computer-readable storage medium, which stores a computer program for executing the above-mentioned reservoir rock permeability prediction method based on the fracture network model.

[0166] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0167] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0168] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0169] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0170] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A reservoir rock permeability prediction method based on a fracture network model, characterized in that: The method comprises: According to the pipeline information of the elliptical cross-section pipeline and the fluid information in the pipeline, a flow calculation model of the elliptical cross-section pipeline under the action of pulsating waves is established, and the flow calculation model includes flow calculation models at the pipeline inlet and outlet: For the established three-dimensional fracture network model, determining the flow calculation equations at both ends of each pipeline in the three-dimensional fracture network model according to the flow calculation model; The flow conservation equations are formulated for the flow calculation equations at both ends of the pipelines at each node in the three-dimensional fracture network model to obtain a flow linear equation group for each node, wherein the node is an intersection point of multiple pipelines; Determine the inlet and outlet pressures of each pipeline according to the linear flow equations of each node; Substitute the inlet and outlet pressures of each pipeline into the flow calculation equation to determine the flow at both ends of each pipeline; Determine the permeability of the three-dimensional fracture network model according to the flow at both ends of each pipeline and the pipeline information; The three-dimensional fracture network model contains fractures, wherein the fractures are pipes for fluid flow, and the three-dimensional fracture network model is established with an ellipse as the fracture shape; The pipeline information of the elliptical cross-section pipeline includes the major axis radius R1, the minor axis radius R2 and the pipeline length L of the elliptical cross-section pipeline section; the fluid information includes the density ρ of the fluid in the pipeline f , the viscosity η of the fluid in the pipe and the speed c of the sound waves in the fluid; According to the pipeline information of the elliptical cross-section pipeline and the fluid information in the pipeline, the flow calculation model of the elliptical cross-section pipeline under the action of pulsating waves is established as follows: Among them, Q Ue , Q De They represent the flow rate at the inlet and outlet of the elliptical cross-section pipe under the action of pulsating waves; a represents the aspect ratio, i represents an imaginary number; P U , P D Respectively represent the pressure at the inlet and outlet of the pipeline; ω represents the frequency; J1(·) represents the first-order Bessel function; J0(·) represents the zero-order Bessel function; R represents the radius of the circular pipeline approximated by the elliptical pipeline; K represents the independent variable coefficient of the Bessel function, λ represents a dimensionless frequency parameter.

2. The method according to claim 1, characterized in that The permeability of the three-dimensional fracture network model is determined according to the flow at both ends of each pipeline and the pipeline information, including: Calculate the total length of all pipes at the outlet of the three-dimensional network model connecting to the outside world, as well as the sum of the cross-sectional areas of the elliptical cross sections of each pipe; The total flow rate at the outlet of the three-dimensional fracture network model connected to the outside world is calculated according to the flow rate at both ends of each pipeline; The permeability of the three-dimensional fracture network model is determined according to the total outlet flow, the total length, the total cross-sectional area, the inlet pressure of the fluid injected into the three-dimensional fracture network model, and the outlet pressure connected to the outside.

3. The method according to claim 2, characterized in that according to Determine the permeability of a three-dimensional fracture network model; Where κ(ω) represents the permeability of the three-dimensional fracture network model when the frequency is ω; ∑Q De represents the total flow rate at the outlet of the three-dimensional fracture network model connected to the outside world; ∑A represents the sum of the cross-sectional areas of the elliptical cross sections of each pipe at the outlet of the three-dimensional network model connected to the outside world, where the cross-sectional area of ​​each pipe is A = aπR1 2 ; ∑L represents the total length of all pipes at the outlet of the three-dimensional network model connected to the outside world; P D ' represents the inlet pressure of the injected fluid in the three-dimensional fracture network model; P U ' represents the outlet pressure of the three-dimensional fracture network model connected to the outside world.

4. A reservoir rock permeability prediction device based on a fracture network model, characterized in that: The device comprises: The model building module is used to establish a flow calculation model of the elliptical cross-section pipeline under the action of pulsating waves according to the pipeline information of the elliptical cross-section pipeline and the fluid information in the pipeline. The flow calculation model includes flow calculation models at the pipeline inlet and outlet: A calculation module, for determining the flow calculation equations at both ends of each pipeline in the three-dimensional fracture network model according to the flow calculation model for the established three-dimensional fracture network model; The calculation module is also used to formulate flow conservation equations for the flow calculation equations at both ends of the pipelines at each node in the three-dimensional fracture network model to obtain a flow linear equation group for each node, wherein the node is an intersection of multiple pipelines; The calculation module is also used to determine the inlet pressure and the outlet pressure of each pipeline according to the flow linear equation group of each node; The calculation module is also used to substitute the inlet pressure and the outlet pressure of each pipeline into the flow calculation equation to determine the flow at both ends of each pipeline; The calculation module is also used to determine the permeability of the three-dimensional fracture network model according to the flow at both ends of each pipeline and the pipeline information; The three-dimensional fracture network model contains fractures, wherein the fractures are pipes for fluid flow, and the three-dimensional fracture network model is established with an ellipse as the fracture shape; The pipeline information of the elliptical cross-section pipeline includes the major axis radius R1, the minor axis radius R2 and the pipeline length L of the elliptical cross-section pipeline section; the fluid information includes the density ρ of the fluid in the pipeline f , the viscosity η of the fluid in the pipe and the speed c of the sound waves in the fluid; The module establishes a flow calculation model for an elliptical cross-section pipeline under the action of a pulsating wave based on the pipeline information of the elliptical cross-section pipeline and the fluid information in the pipeline, as shown below: Among them, Q Ue , Q De They represent the flow rate at the inlet and outlet of the elliptical cross-section pipe under the action of pulsating waves; a represents the aspect ratio, i represents an imaginary number; P U , P D Respectively represent the pressure at the inlet and outlet of the pipeline; ω represents the frequency; J1(·) represents the first-order Bessel function; J0(·) represents the zero-order Bessel function; R represents the radius of the circular pipeline approximated by the elliptical pipeline; K represents the independent variable coefficient of the Bessel function, λ represents a dimensionless frequency parameter.

5. The device according to claim 4, characterized in that Compute module for: Calculate the total length of all pipes at the outlet of the three-dimensional network model connecting to the outside world, as well as the sum of the cross-sectional areas of the elliptical cross sections of each pipe; The total flow rate at the outlet of the three-dimensional fracture network model connected to the outside world is calculated according to the flow rate at both ends of each pipeline; The permeability of the three-dimensional fracture network model is determined according to the total outlet flow, the total length, the total cross-sectional area, the inlet pressure of the fluid injected into the three-dimensional fracture network model, and the outlet pressure connected to the outside.

6. The device according to claim 5, characterized in that Compute module for: according to Determine the permeability of a three-dimensional fracture network model; Where κ(ω) represents the permeability of the three-dimensional fracture network model when the frequency is ω; ∑Q De represents the total flow rate at the outlet of the three-dimensional fracture network model connected to the outside world; ∑A represents the sum of the cross-sectional areas of the elliptical cross sections of each pipe at the outlet of the three-dimensional network model connected to the outside world, where the cross-sectional area of ​​each pipe is A = aπR1 2 ; ∑L represents the total length of all pipes at the outlet of the three-dimensional network model connected to the outside world; P D ' represents the inlet pressure of the injected fluid in the three-dimensional fracture network model; P U ' represents the outlet pressure of the three-dimensional fracture network model connected to the outside world.

7. A computer device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the method according to any one of claims 1 to 3 is implemented.

8. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method according to any one of claims 1 to 3 is implemented.

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