A method for predicting long-term fracture conductivity considering rock creep

Abstract

This invention relates to a method for predicting the long-term conductivity of fractures considering rock creep, comprising the following steps: S1, conducting graded loading creep tests on the rock to obtain rock creep parameters; S2, establishing a rock-proppane-rock physical model; S3, calibrating the physical property parameters of the upper and lower rock slabs; S4, applying closure pressure to the surfaces of the upper and lower rock strata of the model, obtaining the z-coordinates of all spherical particles on the fracture surface, and calculating the fracture width; S5, calculating the permeability of the proppant-filled layer according to the lattice Boltzmann method; S6, calculating the fracture conductivity; S7, repeating steps S3 to S6 to obtain the fracture conductivity at different times. The method of this invention considers the creep characteristics of actual strata, uses different creep parameters for different lithologies, and has a wide range of applications; by combining creep experiments and numerical models to predict the long-term conductivity of fractures, it overcomes the shortcomings of existing indoor experimental methods for predicting conductivity, saves costs, and improves the feasibility of the results.

Description

Technical Field

[0001] This invention relates to the field of oil and gas development, and in particular to a method for predicting the long-term fracture conductivity considering rock creep. Background Technology

[0002] Hydraulic fracturing is a crucial technique for the effective development of low-permeability oil and gas reservoirs. To achieve higher production, the injection-production pressure differential is significant in the initial stages of oil and gas extraction. At this point, the fracture network is under high effective closure pressure, causing proppant particles to embed, deform, and break, and rock creep to occur. This reduces the width of the propped fractures, leading to a decrease in fracture conductivity and a gradual reduction in fracturing profitability. Simultaneously, as oil and gas are continuously extracted, the flow field in the propped fractures changes, causing proppant redistribution. These changes, in turn, affect the flow of fluids and pressure distribution within the fractures, further altering the fracture width and reducing conductivity. Fracture conductivity is not constant but gradually decreases as production progresses.

[0003] Currently, the main methods for evaluating the long-term conductivity of fractures are experimental testing and numerical simulation calculation. Raysoni and Weaver conducted long-term conductivity experiments on sandstone-supported fractures and found that the permeability of the fractures continued to decrease after a long period of time (Rayson N, Weaver J. Improved Understanding of Proppant-Formation Interactions for Sustaining Fracture Conductivity[C]. SPE Saudi Arabia Section Technical Symposium and Exhibition in Al-Khobar, Saudi Arabia, 8-11 April, 2012.). Aven et al. studied the effects of temperature and dynamic fluid flow on the diagenesis of Ohio sandstone-proppant and found that at 288°C for 2-6 months, the permeability of aluminum-based proppant-filled fractures decreased by 40% (Aven NK, Weaver J, Loghry R, ​​et al. Long-Term Dynamic Flow Testing of Proppants and Effect of Coatings[C]. SP European Formation Damage Conference and Exhibition in the Noordwijk, Netherlands, 5-7 June, 2013.). Zhao Yadong conducted a long-term conductivity indoor test on the He 1 reservoir in the Daniudi gas field and found that the conductivity of the fractures decreased by nearly 80% after 55 hours (Zhao Yadong. Study on Long-Term Conductivity of Fracturing Fractures in Tight Sandstone [D]. China University of Petroleum (Beijing), 2017.). In terms of numerical simulation, Khanna et al. established an embedded model of a single-layer proppant using Hertzian contact theory and the superposition principle (Khanna A, Kotousov A, Sobey J, et al. Conductivity of narrow fractures filled with aproppant monolayer [J]. Journal of Petroleum Science and Engineering, 2012, 100.).Guo et al. considered two embedding mechanisms, elastic deformation and creep deformation, and established a mathematical calculation model (Guo J, Liu Y. Modeling of Proppant Embedment: Elastic Deformation and Creep Deformation: SPE International Production and Operations Conference & Exhibition [Z]. Doha, Qatar: Society of Petroleum Engineers, 2012, 8.). Jiao Hongyan established a fracture conductivity prediction model that comprehensively considers the dynamic changes of four factors: proppant embedding, deformation, fracturing, and lithification (Jiao Hongyan. Research and Application of Prediction Model for Decrease in Conductivity of Long Fractures [D]. China University of Petroleum (East China), 2017.). Zhu et al. proposed a new method to predict fracture conductivity using the analytical solution of the discrete element method (Zhu H, Shen J, Zhang FA fracture conductivity model for channel fracturing and its implementation with Discrete Element Method [J]. Journal of Petroleum Science and Engineering, 2018, 172.).

[0004] Most scholars, both domestically and internationally, conduct short-term conductivity experiments. Long-term conductivity measurements are too time-consuming and costly, thus numerical simulation methods are often used. Current numerical simulations primarily consider proppant embedding under pure stress, with less consideration given to rock creep and the fluid-structure interaction between the proppant-filled layer and the fluid.

[0005] Therefore, there is an urgent need to establish a method for predicting the long-term fracture conductivity that takes into account rock creep. This will help to clearly understand the changing patterns of long-term fracture conductivity and provide reference and guidance for the efficient development of low-permeability oil and gas reservoirs. Summary of the Invention

[0006] To overcome the problems in existing technologies, this invention provides a method for predicting long-term fracture conductivity considering rock creep. This method can be combined with the actual conditions of the formation rocks to conveniently and quickly predict the long-term fracture conductivity considering rock creep. To achieve the above objective, this invention provides the following solution:

[0007] A method for predicting the long-term fracture conductivity considering rock creep includes the following steps:

[0008] S1. Conduct graded loading creep tests on rocks to obtain the full-time creep curves of the rocks. Based on the Boltzmann superposition principle, the relationship curves between rock strain and time under different stresses can be obtained by processing the full-time creep curves. By fitting the creep curves of the rocks, the creep parameters of the rocks under different pressures can be obtained by inversion.

[0009] S2. Based on the geological conditions and mechanical characteristics of the rock strata, establish a physical model of the upper rock strata-proppant-lower rock strata that restores the true size of the proppant.

[0010] S3. Calibrate the physical properties of the upper and lower rock strata;

[0011] S4. Apply closing pressure to the surfaces of the upper and lower rock layers in the physical model, obtain the z-coordinates of all spherical particles on the fracture surface, and obtain the effective fracture width H. f ;

[0012] S5. Obtain the permeability k of the proppant-filled layer according to the lattice Boltzmann method;

[0013] S6. Calculate the fracture conductivity FRCD;

[0014] S7. Repeat steps S3 to S6 to obtain the crack conductivity at different times.

[0015] A further technical solution is that the rock creep parameters are obtained through the following process:

[0016] The compressive strength of rock was obtained through uniaxial compression tests and used as the basis for determining the stress levels of each stage of graded loading.

[0017] A graded loading creep test was conducted on the rock to obtain the full-time creep curve of the rock;

[0018] Based on the Boltzmann superposition principle, the creep curves under different stress levels are obtained after processing the full-time creep curves.

[0019] Creep parameters are obtained from the creep curve.

[0020] A further technical solution is that step S4, obtaining the effective width of the crack, includes:

[0021] The z-coordinate of the particle is located within a range of 1 times the diameter of the matrix sphere near the crack surface. The z-coordinates of all spheres within this accuracy range are traversed, and the average z-coordinate of the traversed spheres is marked as [value missing].

[0022] The effective width of a crack under closed stress is the difference between the height of the crack surface in the upper rock and the height of the crack surface in the lower rock. The calculation formula is as follows:

[0023]

[0024]

[0025]

[0026] Where i and j are serial numbers, z i Let z be the height of the i-th coordinate point on the upper rock fracture surface. j The height of the j-th coordinate point on the fracture surface of the lower rock;

[0027] H f The effective width of the crack is in cm;

[0028] The height of the upper rock fissure surface, in cm;

[0029] The height of the lower rock fissure surface, in cm;

[0030] R is the radius of the formation particles, in cm.

[0031] A further technical solution is that step S5 calculates the permeability of the proppant-filled layer according to the lattice Boltzmann method, including:

[0032] The permeability of the proppant-filled layer was calculated using the three-dimensional lattice Boltzmann velocity model D3Q19. The fluid particle flow in the fracture satisfies the single-relaxation-time LB equation based on BGK:

[0033]

[0034]

[0035]

[0036]

[0037]

[0038]

[0039]

[0040] In the formula: i is the specified direction of movement of the lattice: i = 0, 1, 2...18; This is the distribution function of the lattice in the spatial and temporal dimensions; The grid is located in space. The distribution function at time t+Δt; The equilibrium distribution function chosen to recover the macroscopic Navier-Stokes equations; ρ is the density of the lattice at time t; Let be the flow velocity of the lattice at time t; Let be the discrete velocity of the lattice in the i-th direction; Δt be the discrete time step of the lattice; Δx be the lattice spacing; τ be the relaxation time; and υ be the fluid viscosity, m. 2 / s;

[0041] By obtaining the equilibrium distribution function This will give us the distribution function of the grid at a certain location. The equilibrium distribution function is determined by the following equation:

[0042]

[0043] In the formula: w i These are the weighting coefficients;

[0044]

[0045] Obtain the distribution function of the grid at a certain location. Then, the density ρ and flow velocity of the lattice at the macroscopic scale are obtained using the following formulas. And pressure p:

[0046]

[0047]

[0048] p = c S 2 ρ

[0049] c S 2 =c0 2 / 3

[0050] In the formula: p is the fluid pressure; c S c0 is the speed of sound in the lattice; c0 is the speed of sound.

[0051] The feature coefficients are obtained, including feature length, feature time, and feature quality. The calculation formula is as follows:

[0052]

[0053]

[0054]

[0055]

[0056] In the formula: L0 is the characteristic length; L is the actual flow field length, m; N is the number of grids in the LBM lattice flow field; T0 is the characteristic time; υ ​​is the kinematic viscosity in the actual flow field, m. 2 / s; υ0 is the kinematic viscosity of the lattice; M0 is the characteristic mass; ρ is the actual physical density, kg / m³. 3 ρ0 is the lattice density;

[0057] The physical quantities of a real physical system are calculated based on the characteristic coefficients, using the following formula:

[0058]

[0059]

[0060]

[0061]

[0062]

[0063] In the formula: l is the lattice length; t is the lattice time; Δt is the lattice step size; U0 is the macroscopic dimensionless velocity of the fluid; u is the lattice velocity; P is the macroscopic pressure;

[0064] The macroscopic velocity v at the crack length was calculated using the model. x pressure gradient The permeability k of the proppant-filled layer is determined by Darcy's law.

[0065] A further technical solution is that the formula for calculating the fracture conductivity in step S6 is as follows:

[0066] FRCD=H f k

[0067] FRCD stands for fracture conductivity.

[0068] The present invention has the following advantages:

[0069] (1) This invention takes into account the creep characteristics of actual strata and adopts different creep parameters for different lithologies, thus having a wide range of applications.

[0070] (2) By calibrating parameters, this invention corresponds the microscopic parameters of the numerical model with the macroscopic mechanical parameters of the material obtained from indoor experiments, thereby increasing the accuracy of discrete element numerical simulation.

[0071] (3) This invention is highly practical. It predicts the long-term conductivity of cracks by combining creep experiments and numerical models, which overcomes the shortcomings of existing indoor experiments in predicting conductivity, saves costs and improves the feasibility of results.

[0072] (4) This invention reveals the influence of creep effect on the long-term conductivity of fractures, providing theoretical support for the effective development of unconventional oil and gas. Attached Figure Description

[0073] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0074] Figure 1 This is a schematic diagram of crack width under rock creep conditions in an embodiment of the present invention;

[0075] Figure 2 The above are creep curves of rock samples under various stress levels in embodiments of the present invention.

[0076] Figure 3 This is the full-time creep curve of the rock sample in this embodiment of the invention;

[0077] Figure 4 This is a schematic diagram of the physical model of upper rock layer-proppane-lower rock layer in an embodiment of the present invention;

[0078] Figure 5 This is a plan view of the physical model of the upper rock layer-proppant-lower rock layer after servo loading in an embodiment of the present invention;

[0079] Figure 6 The D3Q19 lattice structure in the lattice Boltzmann model is shown in this embodiment of the invention.

[0080] Figure 7 The results of long-term fracture conductivity in a certain block after considering rock creep are presented in an embodiment of the present invention. Detailed Implementation

[0081] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0082] The purpose of this invention is to provide a method for predicting the long-term fracture conductivity considering rock creep. To make the above-mentioned objectives, features and advantages of this invention more apparent and understandable, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0083] A method for predicting the long-term fracture conductivity considering rock creep includes the following steps:

[0084] S1. The compressive strength of the rock was obtained through uniaxial compression tests and used as the basis for determining the stress levels at each stage of graded loading. Then, creep tests were conducted on the rock under graded loading to obtain the full-time creep curve. Based on the Boltzmann superposition principle, the full-time creep curve was processed to obtain the creep curves under each stress level. Finally, the creep parameters were obtained from the creep curves. In this example, the rock's peak strength was 60 MPa, elastic modulus was 38 GPa, and Poisson's ratio was 0.31. The graded loading stresses were 21 MPa, 27 MPa, 34 MPa, 40 MPa, 47 MPa, 51 MPa, and 56 MPa. The full-time creep curve and the creep curves under each stress level are shown below. Figure 2 and Figure 3 This allows us to obtain the variation of rock strain with time under different stresses. A suitable empirical creep model is selected (the Nishihara model is used in this example when σ = 21 MPa) to describe rock creep. The creep equation is:

[0085] ε(t)=0.4+0.127(1-exp(-0.46t)) (1)

[0086] The constitutive equation is:

[0087]

[0088] In the formula, t is time, in hours; σ is stress, in MPa; and ε is strain, in dimensionless units.

[0089] S2. Based on the geological conditions and mechanical characteristics of the rock strata, establish a rock-proppane-rock strata physical model that accurately reflects the size of the proppant. This rock-proppane-rock strata physical model is cubic. To prevent lateral expansion of the sample unit under pressure on the top and bottom surfaces, which would push the pressure plate outwards, the pressure plate and boundaries need to be extended outwards, such as... Figure 4 To prevent the pressure plate from slipping off the side when the sample is uneven, the edge units of the pressure plate must be able to move only along the initial normal direction of the pressure plate. In the aforementioned rock-proppane-rock-layer physical model, the upper particles constitute the upper rock layer 1, the lower particles constitute the lower rock layer 3, and the middle particles constitute the proppane filling layer 2, as shown below. Figure 5 In this example, the proppant has a Poisson's ratio of 0.43 and an elastic modulus of 1.7 GPa, and the sand concentration is 5 kg / m³. 2 The mesh size is 40 / 70.

[0090] S3. Calibrate the physical properties of the upper and lower rock slabs. Based on the triaxial mechanical test results of the rock samples, a discrete element model of the cylindrical rock core is established, and the microscopic parameters are calibrated through a servo process. In this example, the peak strength of the upper rock layer 1 and the lower rock layer 2 is 60 MPa, the elastic modulus is 38 GPa, and the Poisson's ratio is 0.31.

[0091] S4. Apply closing pressure to the surfaces of the upper and lower rock strata of the model to simulate the formation fracture closure process. Define the contact between rock grains using the creep constitutive equation and record the fracture width H. f (t);

[0092] The method for obtaining the crack width is as follows:

[0093] First, the z-coordinate of the particle is located within a range of 1 times the diameter of the matrix sphere near the crack surface. Then, the z-coordinates of all spheres within this accuracy range are traversed, and the average z-coordinate of the traversed spheres at time t is recorded as follows: The effective width of a crack under closed stress is the difference in height between the upper and lower crack surfaces. The calculation formula is:

[0094]

[0095]

[0096]

[0097] Where: H f (t) represents the effective width of the crack at time t, in cm; The height of the upper rock fracture surface at time t, in cm; t represents the height of the rock fracture surface at time t, in cm; R represents the radius of the formation grains, in cm.

[0098] S5. Calculate the permeability of the proppant-filled layer using the lattice Boltzmann method, as follows:

[0099] This invention uses the common three-dimensional lattice Boltzmann velocity model D3Q19 to calculate the permeability of the proppant-filled layer. The flow of fluid particles in the fracture (hereinafter referred to as the fluid particles as the lattice) satisfies the single-relaxation-time LB equation based on BGK:

[0100]

[0101]

[0102]

[0103]

[0104] In the formula: i is the specified direction of movement of the lattice: i = 0, 1, 2...18 (e.g., ...) Figure 6 ); This is the distribution function of the lattice in the spatial and temporal dimensions; The grid is located in space. The distribution function at time t+Δt; The equilibrium distribution function chosen to recover the macroscopic Navier-Stokes equations; ρ is the density of the lattice at time t; Let be the flow velocity of the lattice at time t; Let be the discrete velocity of the lattice in the i-direction, with specific values ​​as shown in equation (7); Δt is the discrete time step of the lattice; Δx is the lattice spacing; τ is the relaxation time; and υ is the fluid viscosity, m. 2 / s;

[0105] By obtaining the equilibrium distribution function This will give us the distribution function of the grid at a certain location. The equilibrium distribution function is determined by equations (10) and (11):

[0106]

[0107] In the formula: w i The weighting coefficient is given by equation (11).

[0108]

[0109] Obtain the distribution function of the grid at a certain location. Then, the density ρ and flow velocity of the lattice at the macroscopic scale are obtained using the following formulas. And pressure p:

[0110]

[0111]

[0112] p = c S 2 ρ (14)

[0113] c S 2 =c0 2 / 3 (15)

[0114] In the formula: p is the fluid pressure; c S c is the speed of sound in the lattice; c0 is the speed of sound, with a magnitude of 340 m / s.

[0115] Given the initial state (t=0), the fluid density ρ inside the fracture is... t＝0 1g / cm 3 At this point, the lattice distribution function is calculated by the following formula:

[0116]

[0117] Calculate the flow velocity at each node according to equation (13). And calculate the equilibrium distribution function at t=0 according to equation (10):

[0118]

[0119] Starting at t=0, each cell begins to move. The cell distribution function at t=Δt is calculated using constant flow boundary conditions:

[0120]

[0121] Combining equations (12), (13), (14), and (18), the density ρ of the lattice at the macroscopic scale at t = Δt is calculated. t＝Δt Flow velocity and pressure p t＝Δt Calculate the equilibrium distribution function at time t = Δt according to equation (10), and begin the second iteration until the convergence condition of equation (19) is met at time t = nΔt (n is a natural number):

[0122]

[0123] In the formula: Let be the flow velocity of the lattice in the x-direction at time t = nΔt; Let be the flow velocity of the lattice in the y direction at time t = nΔt; Let be the flow velocity of the lattice in the z-direction at time t = nΔt; Let be the flow velocity of the lattice in the x-direction at time t = (n-1)Δt; Let be the flow velocity of the lattice in the y direction at time t = (n-1)Δt; Let be the flow velocity of the lattice in the z-direction at time t = (n-1)Δt;

[0124] When the calculation converges, let ρ(t) be the density of the lattice at the macroscopic scale, and let the velocity be... satisfy The pressure is p(t);

[0125] The LBM equations described above are described by lattice points, where all variables are dimensionless. To obtain the actual physical quantities, a series of characteristic factors are needed to perform necessary transformations between the physical system and the lattice system. The characteristic coefficients mainly include characteristic length, characteristic time, and characteristic mass, and their calculation formulas are as follows:

[0126]

[0127]

[0128]

[0129]

[0130] In the formula: L0 is the characteristic length; L is the actual flow field length, m; N is the number of grids in the LBM lattice flow field; T0 is the characteristic time; υ ​​is the kinematic viscosity in the actual flow field, m. 2 / s; υ0 is the kinematic viscosity of the lattice; M0 is the characteristic mass; ρ is the actual physical density, kg / m³. 3 ρ0 is the lattice density;

[0131] The physical quantities of a real physical system are calculated based on the characteristic coefficients, using the following formula:

[0132]

[0133]

[0134]

[0135]

[0136]

[0137] In the formula: l is the lattice length; t is the lattice time; Δt is the lattice step size; U0 is the macroscopic dimensionless velocity of the fluid; u is the lattice velocity; P is the macroscopic pressure;

[0138] The macroscopic velocity v of the fluid at time t along the crack length was calculated using the model. x (t), pressure gradient Then, the permeability is determined using Darcy's Law:

[0139]

[0140] S6. Combining equations (3) and (29), the fracture conductivity K(t) is calculated using the following formula:

[0141] FRCD(t)=H f (t)k(t) (30)

[0142] S7. Repeat steps S3 to S6 to obtain the crack conductivity at different times.

[0143] The above steps achieved an initial loading stress of 21 MPa, a formation Young's modulus of 38 GPa, a Poisson's ratio of 0.31, a fluid viscosity of 1 mPa·s, a proppant Poisson's ratio of 0.43, an elastic modulus of 1.7 GPa, and a proppant concentration of 5 kg / m³. 2 The long-term change in the conductivity of fractures with mesh sizes of 40 / 70, such as Figure 7 As shown.

[0144] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for predicting the long-term fracture conductivity considering rock creep, characterized in that, Includes the following steps: S1. Conduct graded loading creep tests on rocks to obtain the full-time creep curves of the rocks. Based on the Boltzmann superposition principle, process the full-time creep curves to obtain the relationship curves between rock strain and time under different stresses. By fitting the creep curves of the rocks, the creep parameters of the rocks under different pressures are obtained through inversion. S2. Based on the geological conditions and mechanical characteristics of the rock strata, establish a physical model of the upper rock strata-proppant-lower rock strata that restores the true size of the proppant. S3. Calibrate the physical properties of the upper and lower rock strata; S4. Apply closing pressure to the surfaces of the upper and lower rock layers of the physical model, obtain the z-coordinates of all spherical particles on the fracture surface, and obtain the effective fracture width Hf. S5. Obtain the permeability k of the proppant-filled layer according to the lattice Boltzmann method; S6. Calculate the fracture conductivity FRCD; S7. Repeat steps S3 to S6 to obtain the crack conductivity at different times; In step S5, obtaining the proppant-filled layer permeability k according to the lattice Boltzmann method includes: The permeability of the proppant-filled layer was calculated using the three-dimensional lattice Boltzmann velocity model D3Q19. The fluid particle flow in the fracture satisfies the single-relaxation-time LB equation based on BGK: In the formula: i is the specified direction of movement of the lattice: i = 0, 1, 2...18; This is the distribution function of the lattice in the spatial and temporal dimensions; The grid is located in space. The time is The distribution function at time; The equilibrium distribution function chosen to recover the macroscopic Navier-Stokes equation; Let be the density of the lattice at time t; Let be the flow velocity of the lattice at time t; Let be the discrete velocity of the lattice in the i-direction; The discrete time step of the lattice; This refers to the grid spacing; Relaxation time; m is the fluid viscosity. 2 / s; By obtaining the equilibrium distribution function This allows us to obtain the distribution function of the lattice at a certain location. The equilibrium distribution function is determined by the following equation: In the formula: These are the weighting coefficients; Obtain the distribution function of the grid at a certain location. Then, the density of the lattice at the macroscopic scale is calculated using the following formula. Flow velocity And pressure p: In the formula: For fluid pressure; For the speed of sound in a grid; Speed ​​of sound; The feature coefficients are obtained, including feature length, feature time, and feature quality. The calculation formula is as follows: In the formula: L is the characteristic length; N is the actual flow field length (m); N is the number of grids in the LBM lattice flow field. Characteristic time; m is the kinematic viscosity in the actual flow field. 2 / s; The kinematic viscosity of the lattice; Characteristic quality; The actual physical density is kg / m³. 3 , Lattice density; The physical quantities of a real physical system are calculated based on the characteristic coefficients, using the following formula: In the formula: t is the grid length; t is the grid time. The grid step size; Let u be the macroscopic dimensionless velocity of the fluid; let P be the lattice velocity; and let P be the macroscopic pressure. The macroscopic velocity at the crack length was calculated using the model. pressure gradient The permeability k of the proppant-filled layer is determined by Darcy's law.

2. The method for predicting long-term fracture conductivity considering rock creep according to claim 1, further comprising the following step S1: The compressive strength of the rock was obtained through uniaxial compression tests and used as the basis for determining the stress levels of each stage of graded loading. A graded loading creep test was conducted on the rock to obtain the full-time creep curve of the rock; Based on the Boltzmann superposition principle, the creep curves under different stress levels are obtained after processing the full-time creep curves. Creep parameters are obtained from the creep curve.

3. The method for predicting the long-term fracture conductivity considering rock creep according to claim 1, wherein obtaining the effective fracture width in step S4 further includes: The z-coordinate of the particle is located within a range of 1 times the diameter of the matrix sphere near the crack surface. The z-coordinates of all spheres within this accuracy range are traversed, and the average z-coordinate of the traversed spheres is marked as [value missing]. , ; The effective width of a crack under closed stress is the difference between the height of the crack surface in the upper rock and the height of the crack surface in the lower rock. The calculation formula is as follows: Where i and j are sequence numbers, z i Let z be the height of the i-th coordinate point on the upper rock fracture surface. j The height of the j-th coordinate point on the fracture surface of the lower rock; The effective width of the crack is in cm; The height of the upper rock fissure surface, in cm; The height of the lower rock fissure surface, in cm; denoted as , where is the radius of the stratum particles, in cm.

4. The method for predicting long-term fracture conductivity considering rock creep according to claim 1, the formula for calculating fracture conductivity in step S6 is as follows: FRCD stands for fracture conductivity.

5. A computer device, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method for predicting the long-term fracture conductivity considering rock creep as described in any one of claims 1 to 4.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the method for predicting the long-term fracture conductivity considering rock creep as described in any one of claims 1 to 4.

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