Permeability calculation method and system of fracture-cavity medium based on fractal geometry dimension

Abstract

The present invention relates to a method and system for calculating the permeability of fracture-cavity media based on fractal geometric dimensions, the method comprising constructing a fracture-cavity media model of a fracture-cavity porous media sample; calculating the flow parameters of the fracture-cavity porous media sample based on the fracture-cavity media model based on fractal theory; the flow parameters include the cross-sectional area, length and total flow rate of the fracture-cavity porous media sample; substituting the flow parameters into the flow equation of the fracture-cavity porous media sample to calculate the permeability of the fracture-cavity porous media sample. The present invention first constructs a fracture-cavity media model, and then loads the fracture-cavity media model to different degrees based on the fractal theory according to the properties of the fractal structure of the fracture-cavity oil reservoir, calculates the flow parameters under different stresses, and then determines the permeability under different stresses. The present invention realizes accurate prediction of the permeability of fracture-cavity media under the conditions of considering the flow characteristics and fractal characteristics of the fracture-cavity media.

Description

Technical Field

[0001] The invention relates to the technical field of oil reservoir detection, and in particular to a method and system for calculating the permeability of a fracture-cavity medium based on fractal geometric dimensions. Background Art

[0002] With the continuous consumption of fossil energy, the exploration and development of oil resources has been continuously deepened. In recent years, the types of newly discovered oil and gas reservoirs have become more and more complex, and fracture-cavity carbonate reservoirs are one of them. Due to the comprehensive influence of rock structure, post-diagenesis, structural faulting, dissolution, etc. on the reservoir space, the reservoir structure of carbonate reservoirs is very complex and has multi-scale characteristics in space and time, which makes it quite difficult to accurately calculate the permeability of fracture-cavity reservoirs. The quantitative calculation and prediction of carbonate reservoir permeability is an important basis for the efficient development of carbonate oil and gas fields.

[0003] The core measurement method is currently widely used to measure the permeability of fracture-vuggy reservoirs. However, for carbonate rocks with very complex post-diagenetic effects, the randomness of coring causes a large deviation between the final measured value and the actual value. In addition, the well logging or seismic inversion method can only obtain the macro equivalent permeability, and cannot obtain a more precise permeability. Digital image analysis technology requires operations such as electron microscope scanning.

[0004] The permeability model method based on experimental data is a method that uses numerical simulation to solve the permeability. At present, there are two main methods for simulating fractures in fracture-cavity reservoirs. One is the equivalent multiple medium method, which is only suitable for uniformly distributed fractures in a network and cannot accurately simulate the flow of large fractures; the other is the discrete fracture network method, which cannot consider the simultaneous existence of multiple scale fractures and has a huge amount of model calculation. In addition, the numerical method requires cumbersome calculations, which limits its ability to analyze stress sensitivity.

[0005] How to accurately predict the permeability of fracture-cavity media by considering the flow characteristics and fractal characteristics of fracture-cavity media. Summary of the invention

[0006] The purpose of the present invention is to provide a method and system for calculating the permeability of a fracture-hole type medium based on fractal geometry dimension, so as to accurately predict the permeability of the fracture-hole type medium under the conditions of considering the flow characteristics and fractal characteristics of the fracture-hole type medium.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] A method for calculating the permeability of a fracture-cavity medium based on fractal geometry dimension comprises the following steps:

[0009] Constructing a fracture-cavity medium model for fracture-cavity porous medium samples;

[0010] Based on the fractal theory and the fracture-hole type medium model, the flow parameters of the fracture-hole type porous medium sample are calculated; the flow parameters include the cross-sectional area, length and total flow rate of the fracture-hole type porous medium sample;

[0011] The flow parameters are introduced into the flow equation of the fracture-hole type porous medium sample to calculate the permeability of the fracture-hole type porous medium sample; the flow equation is constructed based on Darcy's law.

[0012] Optionally, the flow parameters of the fracture-hole type porous medium sample are calculated based on the fractal theory and the fracture-hole type medium model, specifically including:

[0013] Based on the fractal theory, according to the fracture-hole medium model, using the formula Calculate the cross-sectional area of ​​fracture-cavity porous media samples;

[0014] Based on the fractal theory, according to the fracture-hole medium model, using the formula Calculate the length of the fracture-cavity porous media sample;

[0015] Based on the fractal theory, according to the fracture-hole medium model, using the formula Calculate the total flow rate of fracture-cavity porous media samples;

[0016] Among them, A σ represents the cross-sectional area of ​​the fracture-hole porous medium sample in the fluid flow direction when the stress is σ, E represents Young's modulus, and R0 represents the radius of the fracture-hole porous medium sample when the stress is 0;

[0017] L σ represents the length of the fracture-hole porous medium sample in the direction of fluid flow when the stress is σ, ν represents the Poisson's ratio, L0 represents the length of the fracture-hole porous medium sample in the direction of fluid flow when the stress is 0, Q σ represents the total flow rate of the fluid in the fracture-cavity porous medium sample when the stress is σ, λ maxσ and λ minσ represents the maximum and minimum capillary radius values ​​in the fracture-cavity medium model when the stress is σ; N σ is the number of capillaries in the fracture-hole medium model when the stress is σ, q σ It represents the flow rate of the fluid in a single capillary in the fracture-hole medium model when the stress is σ.

[0018] Optionally, based on the fractal theory and according to the slit-hole medium model, the formula Calculate the total flow rate of the fracture-cavity porous media sample, including:

[0019] Based on the fractal theory, according to the fracture-hole medium model, using the formula Calculate the differential of the number of capillaries in the fracture-cavity medium model when the stress is σ;

[0020] Based on the fractal theory, according to the fracture-hole medium model, using the formula Calculate the flow rate of a single capillary in the fracture-cavity medium model when the stress is σ;

[0021] According to the differential of the number of capillaries in the fracture-hole medium model when the stress is σ and the flow rate of a single capillary in the fracture-hole medium model, the formula is used Calculate the total flow rate of fracture-cavity porous media samples;

[0022] Among them, -dN σ represents the differential of the number of capillaries in the fracture-cavity medium model when the stress is σ, D f represents the capillary fractal dimension in the crack-hole medium model, λ max represents the maximum capillary radius value in the fracture-hole medium model, λ represents the capillary radius variable, q σ represents the flow rate of the fluid in a single capillary in the fracture-hole medium model when the stress is σ, D T represents the bending fractal dimension of the capillary in the crack-hole medium model, C λ represents the stress variation coefficient, Δp represents the pressure difference at both ends of the fracture-hole type medium model, μ represents the viscosity of the fluid in the fracture-hole type porous medium sample, L0 represents the length of the fracture-hole type porous medium sample in the fluid flow direction when the stress is 0, and λ0 represents the capillary radius in the fracture-hole type medium model when the stress is σ.

[0023] Optionally, the flow equation for the fracture-hole porous media sample is:

[0024]

[0025] Among them, K σ represents the permeability of the fracture-cavity porous medium sample when the stress is σ, Q σ represents the total flow rate of the fluid in the fracture-hole porous medium sample when the stress is σ, μ represents the viscosity of the fluid in the fracture-hole porous medium sample, and L σ A represents the length of the fracture-hole porous medium sample in the direction of fluid flow when the stress is σ. σ It represents the cross-sectional area of ​​the crack-hole porous medium sample in the fluid flow direction when the stress is σ, and Δp represents the pressure difference at both ends of the crack-hole medium model.

[0026] A fracture-cavity medium permeability calculation system based on fractal geometry dimension, comprising:

[0027] A fracture-hole medium model construction module is used to construct a fracture-hole medium model for fracture-hole porous medium samples;

[0028] A flow parameter calculation module, for calculating the flow parameters of the fracture-hole type porous medium sample based on the fractal theory and the fracture-hole type medium model; the flow parameters include the cross-sectional area, length and total flow of the fracture-hole type porous medium sample;

[0029] The permeability calculation module is used to bring the flow parameters into the flow equation of the fracture-hole type porous medium sample to calculate the permeability of the fracture-hole type porous medium sample; the flow equation is constructed based on Darcy's law.

[0030] Optionally, the flow parameter calculation module specifically includes:

[0031] The cross-sectional area calculation submodule is used to calculate the cross-sectional area based on the fractal theory and the crack-hole medium model using the formula Calculate the cross-sectional area of ​​fracture-cavity porous media samples;

[0032] The length calculation submodule is used to calculate the length of the crack-hole medium model based on the fractal theory using the formula Calculate the length of the fracture-cavity porous media sample;

[0033] The total flow calculation submodule is used to calculate the total flow rate based on the fractal theory and the crack-hole medium model using the formula Calculate the total flow rate of fracture-cavity porous media samples;

[0034] Among them, A σ represents the cross-sectional area of ​​the fracture-hole porous medium sample in the fluid flow direction when the stress is σ, E represents Young's modulus, and R0 represents the radius of the fracture-hole porous medium sample when the stress is 0;

[0035] L σ represents the length of the fracture-hole porous medium sample in the direction of fluid flow when the stress is σ, ν represents the Poisson's ratio, and L0 represents the length of the fracture-hole porous medium sample in the direction of fluid flow when the stress is 0;

[0036] Q σ represents the total flow rate of the fluid in the fracture-cavity porous medium sample when the stress is σ, λ maxσ and λ minσ represents the maximum and minimum capillary radius values ​​in the fracture-cavity medium model when the stress is σ; N σ is the number of capillaries in the fracture-hole medium model when the stress is σ, q σ It represents the flow rate of the fluid in a single capillary in the fracture-hole medium model when the stress is σ.

[0037] Optionally, the total flow calculation submodule specifically includes:

[0038] The differential solution unit of the number of capillaries is used to calculate the number of capillaries based on the fractal theory and the crack-hole medium model using the formula Calculate the differential of the number of capillaries in the fracture-cavity medium model when the stress is σ;

[0039] The flow calculation unit of a single capillary is used to calculate the flow rate of a single capillary based on the fractal theory and the crack-hole medium model using the formula Calculate the flow rate of a single capillary in the fracture-cavity medium model when the stress is σ;

[0040] The total flow calculation unit is used to calculate the total flow rate according to the differential of the number of capillaries in the fracture-hole medium model and the flow rate of a single capillary in the fracture-hole medium model when the stress is σ, using the formula Calculate the total flow rate of fracture-cavity porous media samples;

[0041] Among them, -dN σ represents the differential of the number of capillaries in the fracture-cavity medium model when the stress is σ, D f represents the capillary fractal dimension in the crack-hole medium model, λ max represents the maximum capillary radius value in the fracture-hole medium model, λ represents the capillary radius variable, q σ represents the flow rate of the fluid in a single capillary in the fracture-hole medium model when the stress is σ, D T represents the bending fractal dimension of the capillary in the crack-hole medium model, C λ represents the stress variation coefficient, Δp represents the pressure difference at both ends of the fracture-hole type medium model, μ represents the viscosity of the fluid in the fracture-hole type porous medium sample, L0 represents the length of the fracture-hole type porous medium sample in the fluid flow direction when the stress is 0, and λ0 represents the capillary radius in the fracture-hole type medium model when the stress is σ.

[0042] Optionally, the flow equation for the fracture-hole porous media sample is:

[0043]

[0044] Among them, K σ represents the permeability of the fracture-cavity porous medium sample when the stress is σ, Q σ represents the total flow rate of the fluid in the fracture-hole porous medium sample when the stress is σ, μ represents the viscosity of the fluid in the fracture-hole porous medium sample, and L σ A represents the length of the fracture-hole porous medium sample in the direction of fluid flow when the stress is σ. σ It represents the cross-sectional area of ​​the crack-hole porous medium sample in the fluid flow direction when the stress is σ, and Δp represents the pressure difference at both ends of the crack-hole medium model.

[0045] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0046] The present invention discloses a method and system for calculating the permeability of fracture-cavity media based on fractal geometric dimension, the method comprising the following steps: constructing a fracture-cavity media model of a fracture-cavity porous media sample; based on the fractal theory, calculating the flow parameters of the fracture-cavity porous media sample according to the fracture-cavity media model; the flow parameters include the cross-sectional area, length and total flow of the fracture-cavity porous media sample; substituting the flow parameters into the flow equation of the fracture-cavity porous media sample to calculate the permeability of the fracture-cavity porous media sample; the flow equation is constructed based on Darcy's law. The present invention first constructs a fracture-cavity media model, and then loads the fracture-cavity media model to different degrees according to the properties of the fractal structure of the fracture-cavity oil reservoir, based on the fractal theory, and calculates the flow parameters under different stresses, and then the permeability under different stresses can be determined. The present invention realizes accurate prediction of the permeability of fracture-cavity media under the conditions of considering the flow characteristics and fractal characteristics of fracture-cavity media. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. 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 paying creative labor.

[0048] Figure 1 A flow chart of a method for calculating the permeability of a fracture-cavity medium based on fractal geometry dimension provided by the present invention;

[0049] Figure 2 A schematic diagram of a method for calculating the permeability of a fracture-cavity medium based on fractal geometric dimension provided by the present invention;

[0050] Figure 3 A schematic diagram of the structure of the slit-hole medium model provided by the present invention;

[0051] Figure 4 This is a schematic structural diagram of the thick-walled cylinder model provided by the present invention. DETAILED DESCRIPTION

[0052] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0053] The purpose of the present invention is to provide a method and system for calculating the permeability of a fracture-hole type medium based on fractal geometry dimension, so as to accurately predict the permeability of the fracture-hole type medium under the conditions of considering the flow characteristics and fractal characteristics of the fracture-hole type medium.

[0054] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0055] like Figure 1 and 2 As shown, the present invention provides a method for calculating the permeability of a fracture-cavity medium based on fractal geometry dimension, comprising the following steps:

[0056] Step 101, constructing a fracture-hole type medium model of a fracture-hole type porous medium sample.

[0057] The underground reservoir rock of the fracture-cavity oil reservoir is a material composed of a solid skeleton and interconnected pores, cracks, and caves, that is, porous media. Since the microstructure of porous media is disordered and extremely complex, it is difficult to obtain analytical solutions for the permeability and porosity of porous media. A large number of studies have shown that naturally formed porous media are fractal structures, that is, the pore size distribution or the pore and solid microstructure are fractal structures, or both are approximately fractal, so fractal theory can be introduced to describe the microstructure of porous media.

[0058] Considering the actual migration state of fluid in fracture-cavity media, a new permeability fractal model considering the elastic-plastic deformation of fracture-cavity media under stress-sensitive conditions is established based on material mechanics and fractal characteristics according to the characteristics of fracture-cavity media, namely, the fracture-cavity media model. The obtained fracture-cavity media model is as follows: Figure 3 shown.

[0059] The fluid channels in porous media can be regarded as curved capillaries with different radii. The following assumptions are made for the slit-hole porous media sample: (1) The fluid channels in porous media can be regarded as curved capillaries with different radii. (2) When the slit-hole porous media sample is under pressure, the internal capillary flow channels are subjected to uniform stress. (3) After deformation, the total number of capillaries in the porous media remains unchanged. (4) The stress-strain and fluid flow in the porous media are steady-state. (5) The porous media is an ideal elastoplastic body.

[0060] Step 102, based on fractal theory and according to the fracture-hole type porous medium model, the flow parameters of the fracture-hole type porous medium sample are calculated; the flow parameters include the cross-sectional area, length and total flow rate of the fracture-hole type porous medium sample.

[0061] A large number of studies have shown that the length, pore size and number of curved capillaries in porous media all satisfy the fractal scaling law, that is, the fractal geometry theory. The basic relationship is that the measure M(ε) of the fractal object and the measured scale ε obey the following scaling relationship:

[0062]

[0063] Where D f is the fractal dimension. M(ε) can be the mass, volume, area or length of a curve, and ε is the scale of measurement. The equation shows that when the measurement scale ε changes, the measurement M(ε) of the fractal object changes accordingly, but the fractal dimension D f The value of remains unchanged, that is, it is a constant.

[0064] According to assumption (2), when the fracture-cavity porous media sample is under pressure, the internal capillary flow channel is subjected to uniform stress. The thick-walled cylinder model can analyze the capillary deformation caused by stress, such as Figure 4 According to experimental data, the change in permeability caused by stress is irreversible, so the microstructure of the porous medium should have undergone permanent changes, which can be characterized by the elastic-plastic deformation of the capillary cross-sectional area in the capillary bundle model.

[0065] According to material mechanics, considering the stress changes in the elastic and plastic zones of the thick-walled cylinder, the capillary radius can be calculated to be

[0066] λ σ =(1+C λ )λ0 (2)

[0067] In the formula, λ σ is the capillary radius when the stress is σ, λ0 is the capillary radius when the stress is equal to 0, C λ is a parameter that changes with stress. λ ≤σ a When C λ =C eλ ; When σ a <σ λ ≤σ b When C λ =C pλ ; When σ λ >σ b When C λ =C pλ (σ b ). The present invention adopts the Tresca yield criterion. σ λ >σ b The expression C in λ =C pλ (σ b) means assuming that when the stress exceeds the plastic limit of the capillary, the radius of the capillary in the cross-sectional area will not deform further. This assumption is made because according to assumption (5) the porous medium is an ideal elastic-plastic body. When the stress exceeds the plastic stress limit, the capillary will deform indefinitely and the porosity and permeability will be zero. However, in actual situations, due to rock crushing or other reasons, the porous medium still maintains a certain permeability and porosity. Therefore, this assumption makes the model consistent with the actual situation.

[0068] 1. Capillary length

[0069] The capillary is curved in the porous medium, and the relationship between the capillary radius change and the length can be established by describing the change in the length of the capillary bundle of the entire sample. When the stress is equal to 0, the fracture-hole porous medium sample is a cylinder with a radius of R0 and a length of L0, such as Figure 3 According to Hooke's law

[0070]

[0071] In the formula, R σ is the radius of the fracture-hole porous medium sample when the stress is equal to σ, σ is the stress, E is the Young's modulus, and R0 is the radius of the fracture-hole porous medium sample when the stress is 0.

[0072] Therefore, the cross-sectional area of ​​the crack-hole porous medium sample considering the cross-sectional stress can be expressed as

[0073]

[0074] Similarly, the length of the fracture-hole porous medium sample considering stress is

[0075]

[0076] Where L0 is the length of the fracture-cavity porous medium sample when the stress is 0, and ν is the Poisson’s ratio.

[0077] According to the fractal scaling law, the capillary length is

[0078]

[0079] Where, L p is the capillary length, D T is the bending fractal dimension of the capillary, and L0 is the characteristic length, i.e., the length of the fracture-hole porous medium sample.

[0080] So when considering stress, the capillary length can be expressed as

[0081]

[0082] 2. Capillary fractal

[0083] According to fractal theory, the cumulative number and size of pores with pore diameters greater than or equal to λ in porous media satisfy the following fractal scaling relationship:

[0084]

[0085] In the formula, N is the number of capillaries, l is the radius of a capillary, and D f is the fractal dimension, λ max is the maximum pore radius in the porous medium, where 0 <D f <2 (in two-dimensional space), or 0 <D f <3 (in three-dimensional space). f =2, it represents a smooth plane; when D f =3, it represents a three-dimensional object.

[0086] Differentiate (8) to obtain

[0087]

[0088] Taking the logarithm of (8), we get the capillary fractal dimension

[0089]

[0090] Obviously, the number of capillaries in a porous medium does not change, so

[0091] N=N0=N σ (11)

[0092] Where N0 is the number of capillaries when the stress is equal to 0, N σ is the number of capillaries when the stress is equal to σ.

[0093] Therefore, from formula (9), when considering stress

[0094]

[0095] From equations (10) and (11), we can get that when stress is not considered

[0096]

[0097] Where D fσ Represents the capillary fractal dimension when the stress is equal to σ.

[0098] When the stress is σ

[0099]

[0100] Where D f0Represents the fractal dimension when stress equals 0

[0101] Therefore, from equations (10), (11), (12), and (13), we can get

[0102] D fσ =D f0 =D f (15)

[0103] 3. Total flow rate of crack-hole porous media samples

[0104] According to Poiseuille's equation, the flow rate q in a single capillary can be expressed as

[0105]

[0106] Where μ is the viscosity, Δp is the pressure difference, λ is the capillary radius, and L p is the capillary length.

[0107] When the stress is σ, the flow rate in a single capillary considering the stress is obtained from equation (16):

[0108]

[0109] Substituting equations (2) and (7) into equation (17), we can calculate

[0110]

[0111] When considering stress, the total flow rate Q through the crack-type porous medium sample is σ It can be obtained by integrating the flow from the smallest diameter capillary to the largest diameter capillary.

[0112]

[0113] Substituting equations (12) and (18) into equation (19), we can obtain

[0114]

[0115] Step 103, bringing the flow parameters into the flow equation of the fracture-hole type porous medium sample to calculate the permeability of the fracture-hole type porous medium sample; the flow equation is constructed based on Darcy's law.

[0116] The permeability of porous media can be expressed by the following Darcy equation:

[0117]

[0118] When the stress is σ, it can be obtained from formula (21) that when considering the stress, the Darcy equation of the fracture-cavity porous medium sample is:

[0119]

[0120] In the formula, Q σ represents the total flow rate through the fracture-type porous medium sample when the stress is σ, μ represents the viscosity of the fluid, and L σ A represents the length of the fracture-hole porous medium sample in the flow direction when the stress is σ. σ It represents the cross-sectional area of ​​the fracture-hole porous medium sample in the flow direction when the stress is σ, and Δp represents the pressure difference at both ends of the model.

[0121] In step 102, the various flow parameters of the fracture-hole type porous medium sample have been solved. Substituting equations (4), (5), and (20) into equation (22), the permeability of the fracture-hole type porous medium sample can be calculated when stress is considered.

[0122]

[0123] Similarly, the permeability of the fracture-cavity porous medium sample when the stress is 0 can be deduced:

[0124]

[0125] The embodiment of the present invention uses the following method to verify the method of the present invention:

[0126] The fractal parameter D of the core can be obtained by CT scanning. f and D T Other physical quantities can be obtained by consulting data or measuring according to the type of core, and then the core permeability is calculated. The permeability calculation results of the present invention are compared with experimental data and existing permeability calculation empirical models to verify the accuracy of the proposed method for calculating permeability of fracture-cavity media.

[0127] The embodiment of the present invention further provides a fracture-cavity medium permeability calculation system based on fractal geometry dimension, comprising:

[0128] The fracture-hole type medium model construction module is used to construct the fracture-hole type medium model of the fracture-hole type porous medium sample.

[0129] The flow parameter calculation module is used to calculate the flow parameters of the fracture-hole type porous medium sample based on the fractal theory and the fracture-hole type medium model; the flow parameters include the cross-sectional area, length and total flow rate of the fracture-hole type porous medium sample.

[0130] The flow parameter calculation module specifically includes:

[0131] The cross-sectional area calculation submodule is used to calculate the cross-sectional area based on the fractal theory and the crack-hole medium model using the formula Calculate the cross-sectional area of ​​porous media samples with cracks and holes.

[0132] The length calculation submodule is used to calculate the length of the crack-hole medium model based on the fractal theory using the formula Calculate the length of the porous media sample with cracks and holes.

[0133] The total flow calculation submodule is used to calculate the total flow rate based on the fractal theory and the crack-hole medium model using the formula Calculate the total flow rate of porous media samples with fractures and holes.

[0134] Among them, A σ It represents the cross-sectional area of ​​the fracture-hole porous medium sample in the fluid flow direction when the stress is σ, E represents Young's modulus, and R0 represents the radius of the fracture-hole porous medium sample when the stress is 0.

[0135] L σ It represents the length of the fracture-hole porous medium sample in the direction of fluid flow when the stress is σ, ν represents the Poisson's ratio, and L0 represents the length of the fracture-hole porous medium sample in the direction of fluid flow when the stress is 0.

[0136] Q σ represents the total flow rate of the fluid in the fracture-cavity porous medium sample when the stress is σ, λ maxσ and λ minσ represents the maximum and minimum capillary radius values ​​in the fracture-cavity medium model when the stress is σ; N σ is the number of capillaries in the fracture-hole medium model when the stress is σ, q σ It represents the flow rate of the fluid in a single capillary in the fracture-hole medium model when the stress is σ.

[0137] The total flow calculation submodule specifically includes:

[0138] The differential solution unit of the number of capillaries is used to calculate the number of capillaries based on the fractal theory and the crack-hole medium model using the formula Calculate the differential of the number of capillaries in the fracture-cavity medium model when the stress is σ.

[0139] The flow calculation unit of a single capillary is used to calculate the flow rate of a single capillary based on the fractal theory and the crack-hole medium model using the formula Calculate the flow rate of a single capillary in the fracture-cavity medium model when the stress is σ.

[0140] The total flow calculation unit is used to calculate the total flow rate according to the differential of the number of capillaries in the fracture-hole medium model and the flow rate of a single capillary in the fracture-hole medium model when the stress is σ, using the formula Calculate the total flow rate of porous media samples with fractures and holes.

[0141] Among them, -dN σrepresents the differential of the number of capillaries in the fracture-cavity medium model when the stress is σ, D f represents the capillary fractal dimension in the crack-hole medium model, λ max represents the maximum capillary radius value in the fracture-hole medium model, λ represents the capillary radius variable, q σ represents the flow rate of the fluid in a single capillary in the fracture-hole medium model when the stress is σ, D T represents the bending fractal dimension of the capillary in the crack-hole medium model, C λ represents the stress variation coefficient, Δp represents the pressure difference at both ends of the fracture-hole type medium model, μ represents the viscosity of the fluid in the fracture-hole type porous medium sample, L0 represents the length of the fracture-hole type porous medium sample in the fluid flow direction when the stress is 0, and λ0 represents the capillary radius in the fracture-hole type medium model when the stress is σ.

[0142] The permeability calculation module is used to bring the flow parameters into the flow equation of the fracture-hole type porous medium sample to calculate the permeability of the fracture-hole type porous medium sample; the flow equation is constructed based on Darcy's law.

[0143] The flow equation of the fracture-hole porous medium sample is:

[0144]

[0145] Among them, K σ represents the permeability of the fracture-cavity porous medium sample when the stress is σ, Q σ represents the total flow rate of the fluid in the fracture-hole porous medium sample when the stress is σ, μ represents the viscosity of the fluid in the fracture-hole porous medium sample, and L σ A represents the length of the fracture-hole porous medium sample in the direction of fluid flow when the stress is σ. σ It represents the cross-sectional area of ​​the crack-hole porous medium sample in the fluid flow direction when the stress is σ, and Δp represents the pressure difference at both ends of the crack-hole medium model.

[0146] The embodiment of the present invention uses the following method to verify the method and system of the present invention:

[0147] The fractal parameter D of the core can be obtained by CT scanning. f and D T Other physical quantities can be obtained by consulting data or measuring according to the type of core, and then the core permeability is calculated. The permeability calculation results of the present invention are compared with experimental data and existing permeability calculation empirical models to verify the accuracy of the proposed method for calculating permeability of fracture-cavity media.

[0148] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0149] 1. The present invention establishes a fracture-cavity medium permeability model based on fractal theory and derives a mathematical characterization equation for the fracture-cavity medium permeability. Compared with numerical simulation, well logging and other methods, the proposed fracture-cavity medium permeability calculation model is simpler, has a faster calculation speed, and has a wider range of applications, which greatly reduces the cost of shale permeability prediction.

[0150] 2. For fracture-cavity porous media, a permeability prediction formula that takes into account the fractal dimension is derived and established. Taking into account stress sensitivity, the permeability of fracture-cavity media can be accurately predicted under the conditions of all flow characteristics and fractal characteristics in fracture-cavity media. There is no need for complex electron microscope scanning or numerical simulation, and the permeability can be accurately predicted through simple calculations. And it has higher accuracy under high stress conditions, and can predict the permeability changes caused by the elastic-plastic deformation of fractal porous media under loading-unloading stress cycles. The present invention has important reference and guiding significance for fracture-cavity reservoir capacity prediction, experimental simulation, and fracture-cavity media seepage mechanism research.

[0151] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0152] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for calculating the permeability of fracture-cavity media based on fractal geometry dimension, characterized in that: The steps include: Constructing a fracture-cavity medium model for fracture-cavity porous medium samples; Based on the fractal theory and the fracture-hole type medium model, the flow parameters of the fracture-hole type porous medium sample are calculated; the flow parameters include the cross-sectional area, length and total flow rate of the fracture-hole type porous medium sample; Substituting the flow parameters into the flow equation of the fracture-hole type porous medium sample to calculate the permeability of the fracture-hole type porous medium sample; the flow equation is constructed based on Darcy's law; The method of calculating the flow parameters of the fracture-hole porous medium sample based on the fractal theory and the fracture-hole medium model specifically includes: Based on the fractal theory, according to the fracture-hole medium model, using the formula Calculate the cross-sectional area of ​​fracture-cavity porous media samples; Based on the fractal theory, according to the fracture-hole medium model, using the formula Calculate the length of the fracture-cavity porous media sample; Based on the fractal theory, according to the fracture-hole medium model, using the formula Calculate the total flow rate of fracture-cavity porous media samples; Among them, A σ represents the cross-sectional area of ​​the fracture-hole porous medium sample in the fluid flow direction when the stress is σ, E represents Young's modulus, and R0 represents the radius of the fracture-hole porous medium sample when the stress is 0; L σ represents the length of the fracture-hole porous medium sample in the direction of fluid flow when the stress is σ, ν represents the Poisson's ratio, L0 represents the length of the fracture-hole porous medium sample in the direction of fluid flow when the stress is 0, Q σ represents the total flow rate of the fluid in the fracture-cavity porous medium sample when the stress is σ, λ maxσ and λ minσ represents the maximum and minimum capillary radius values ​​in the fracture-cavity medium model when the stress is σ; N σ is the number of capillaries in the fracture-hole medium model when the stress is σ, q σ It represents the flow rate of the fluid in a single capillary in the fracture-hole medium model when the stress is σ; Based on the fractal theory, according to the crack-hole medium model, using the formula Calculate the total flow rate of the fracture-cavity porous media sample, including: Based on the fractal theory, according to the fracture-hole medium model, using the formula Calculate the differential of the number of capillaries in the fracture-cavity medium model when the stress is σ; Based on the fractal theory, according to the fracture-hole medium model, using the formula Calculate the flow rate of a single capillary in the fracture-cavity medium model when the stress is σ; According to the differential of the number of capillaries in the fracture-hole medium model when the stress is σ and the flow rate of a single capillary in the fracture-hole medium model, the formula is used Calculate the total flow rate of fracture-cavity porous media samples; Among them, -dN σ represents the differential of the number of capillaries in the fracture-cavity medium model when the stress is σ, D f represents the capillary fractal dimension in the crack-hole medium model, λ max represents the maximum capillary radius value in the fracture-hole medium model, λ represents the capillary radius variable, and D T represents the bending fractal dimension of the capillary in the crack-hole medium model, C λ represents the stress variation coefficient, Δp represents the pressure difference at both ends of the fracture-hole type medium model, μ represents the viscosity of the fluid in the fracture-hole type porous medium sample, and λ0 represents the capillary radius in the fracture-hole type medium model when the stress is σ; The flow equation of the fracture-hole porous medium sample is: Among them, K σ represents the permeability of the fracture-cavity porous medium sample when the stress is σ, Q σ represents the total flow rate of the fluid in the fracture-hole porous medium sample when the stress is σ, μ represents the viscosity of the fluid in the fracture-hole porous medium sample, and L σ A represents the length of the fracture-hole porous medium sample in the direction of fluid flow when the stress is σ. σ It represents the cross-sectional area of ​​the crack-hole porous medium sample in the fluid flow direction when the stress is σ, and Δp represents the pressure difference at both ends of the crack-hole medium model.

2. A fracture-cavity medium permeability calculation system based on fractal geometry dimension, characterized in that: include: A fracture-hole medium model construction module is used to construct a fracture-hole medium model for fracture-hole porous medium samples; A flow parameter calculation module, for calculating the flow parameters of the fracture-hole type porous medium sample based on the fractal theory and the fracture-hole type medium model; the flow parameters include the cross-sectional area, length and total flow of the fracture-hole type porous medium sample; A permeability calculation module, used for bringing the flow parameters into the flow equation of the fracture-hole type porous medium sample to calculate the permeability of the fracture-hole type porous medium sample; The flow equation is constructed based on Darcy's law; The flow parameter calculation module specifically includes: The cross-sectional area calculation submodule is used to calculate the cross-sectional area based on the fractal theory and the crack-hole medium model using the formula Calculate the cross-sectional area of ​​fracture-cavity porous media samples; The length calculation submodule is used to calculate the length of the crack-hole medium model based on the fractal theory using the formula Calculate the length of the fracture-cavity porous media sample; The total flow calculation submodule is used to calculate the total flow rate based on the fractal theory and the crack-hole medium model using the formula Calculate the total flow rate of fracture-cavity porous media samples; Among them, A σ represents the cross-sectional area of ​​the fracture-hole porous medium sample in the fluid flow direction when the stress is σ, E represents Young's modulus, and R0 represents the radius of the fracture-hole porous medium sample when the stress is 0; L σ represents the length of the fracture-hole porous medium sample in the direction of fluid flow when the stress is σ, ν represents the Poisson's ratio, and L0 represents the length of the fracture-hole porous medium sample in the direction of fluid flow when the stress is 0; Q σ represents the total flow rate of the fluid in the fracture-cavity porous medium sample when the stress is σ, λ maxσ and λ minσ represents the maximum and minimum capillary radius values ​​in the fracture-cavity medium model when the stress is σ; N σ is the number of capillaries in the fracture-hole medium model when the stress is σ, q σ It represents the flow rate of the fluid in a single capillary in the fracture-hole medium model when the stress is σ; The total flow calculation submodule specifically includes: The differential solution unit of the number of capillaries is used to calculate the number of capillaries based on the fractal theory and the crack-hole medium model using the formula Calculate the differential of the number of capillaries in the fracture-cavity medium model when the stress is σ; The flow calculation unit of a single capillary is used to calculate the flow rate of a single capillary based on the fractal theory and the crack-hole medium model using the formula Calculate the flow rate of a single capillary in the fracture-cavity medium model when the stress is σ; The total flow calculation unit is used to calculate the total flow rate according to the differential of the number of capillaries in the fracture-hole medium model and the flow rate of a single capillary in the fracture-hole medium model when the stress is σ, using the formula Calculate the total flow rate of fracture-cavity porous media samples; Among them, -dN σ represents the differential of the number of capillaries in the fracture-cavity medium model when the stress is σ, D f represents the capillary fractal dimension in the crack-hole medium model, λ max represents the maximum capillary radius value in the fracture-hole medium model, λ represents the capillary radius variable, and D T represents the bending fractal dimension of the capillary in the crack-hole medium model, C λ represents the stress variation coefficient, Δp represents the pressure difference at both ends of the fracture-hole type medium model, μ represents the viscosity of the fluid in the fracture-hole type porous medium sample, and λ0 represents the capillary radius in the fracture-hole type medium model when the stress is σ; The flow equation of the fracture-hole porous medium sample is: Among them, K σ represents the permeability of the fracture-cavity porous medium sample when the stress is σ, Q σ represents the total flow rate of the fluid in the fracture-hole porous medium sample when the stress is σ, μ represents the viscosity of the fluid in the fracture-hole porous medium sample, and L σ A represents the length of the fracture-hole porous medium sample in the direction of fluid flow when the stress is σ. σ It represents the cross-sectional area of ​​the crack-hole porous medium sample in the fluid flow direction when the stress is σ, and Δp represents the pressure difference at both ends of the crack-hole medium model.

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