A shale reservoir repeated fracturing stress-crack redirection simulation method and system

Abstract

The present invention discloses a shale reservoir refracturing stress-crack redirection simulation method and system. By establishing a hydraulic fracture random expansion and fracture deformation stress field model, the method realizes the simulation of the fracture deformation induced stress field under complex fracture morphology and the simulation of the hydraulic fracture random expansion under non-uniform stress field conditions. The method further establishes a fluid-solid coupled horizontal well seepage model to realize the simulation of the entire process of "initial fracturing crack expansion-production after initial fracturing-refracturing crack expansion-production after refracturing" in the shale reservoir. The method can not only be used for shale gas refracturing stress-crack redirection simulation, but also for the optimization of shale gas refracturing timing, well and layer selection, and optimized design based on production capacity, thereby improving the adaptability of the shale gas refracturing process, reducing the risk of field operations, and also facilitating the improvement or restoration of shale gas well production capacity and the ultimate recovery rate of the reservoir.

Description

Technical Field

[0001] The present invention relates to the technical field of unconventional oil and gas extraction, and in particular to a method and system for simulating stress-crack redirection in repeated fracturing of shale reservoirs. Background Art

[0002] During the early stages of shale gas exploration and development, limitations and deviations in reservoir understanding may lead to mismatches between the optimized design of fracturing wells and process implementation and reservoir location conditions, resulting in insufficient reservoir transformation, poor initial fracturing effects, or rapid post-fracturing production decline. At the same time, the loss of hydraulic fracture conductivity during production also limits gas extraction, reducing the ultimate recovery rate of shale gas reservoirs.

[0003] To address these issues, the industry has developed refracturing technology for shale gas horizontal wells. This involves using temporary plugging techniques like chemical or mechanical isolation, followed by secondary fracturing. This reconstructs the fracture network, expands the stimulated area, and increases the fracture network load. This, in turn, increases or restores shale gas well productivity and improves ultimate reservoir recovery. Compared to deploying infill wells, refracturing shale gas horizontal wells not only reduces interwell fractures and production disruptions, but also reduces new well drilling costs by 30% to 40%.

[0004] However, the existing shale gas horizontal well repeated fracturing technology is still in the exploration and testing stage. When using the existing shale gas horizontal well repeated fracturing technology for field construction, it will face problems such as poor process adaptability and high operation risks.

[0005] In view of this, this application is hereby filed. Summary of the Invention

[0006] The technical problem to be solved by the present invention is that when the existing shale gas horizontal well repeated fracturing technology is used for on-site construction, the problems of poor process adaptability and high operational risks are encountered. The purpose is to provide a shale reservoir repeated fracturing stress-crack redirection simulation method and system. By establishing a hydraulic fracture random expansion and fracture deformation stress field model, the fracture deformation induced stress field simulation under complex fracture morphology and the hydraulic fracture random expansion simulation under non-uniform stress field conditions are realized. Further, a fluid-solid coupled horizontal well seepage model is established to realize the full process simulation of the shale reservoir "initial fracturing crack expansion-production after initial fracturing-repeated fracturing crack expansion-production after repeated fracturing", thereby forming a complete set of shale gas horizontal well repeated fracturing technology for shale gas repeated fracturing process flow analysis and reducing operational risks.

[0007] The stress field before fracturing and the new fracture redirection problem are analyzed repeatedly during the simulation process.

[0008] The present invention is achieved through the following technical solutions:

[0009] In one aspect, the present invention provides a method for simulating stress-crack redirection in refracturing a shale reservoir, comprising the following steps:

[0010] Establishing a hydraulic fracture random propagation model and initializing model parameters; performing an initial hydraulic fracture random propagation simulation based on the hydraulic fracture random propagation model and the model parameters to obtain an initial fracture morphology;

[0011] Conducting a production fracture conductivity loss evaluation experiment based on the initial fracture morphology to obtain experimental results, wherein the experimental results include: a relationship between the propped fracture width and the effective closure stress, and a relationship between the propped fracture conductivity loss and the effective closure stress;

[0012] Performing a total stress field simulation before refracturing based on the experimental results to obtain initial closed fracture deformation induced stress and reservoir production induced stress; linearly superimposing the initial closed fracture deformation induced stress and the reservoir production induced stress to obtain the total stress field before refracturing;

[0013] In the total stress field before refracturing, refracturing fracture propagation simulation is performed according to the hydraulic fracture random propagation model to obtain shale reservoir refracturing stress-crack redirection simulation results.

[0014] By establishing a model for the random propagation of hydraulic fractures and the stress field of fracture deformation, the method proposed in this paper simulates the stress field induced by fracture deformation under complex fracture morphologies and the random propagation of hydraulic fractures under non-uniform stress conditions. Furthermore, based on an accurate description of gas migration patterns in multi-scale shale gas reservoirs, a fluid-solid coupled horizontal well flow model was established. Based on linear elasticity, fracture mechanics, seepage mechanics, and experimental evaluation, the entire process of shale reservoir formation—from initial fracturing to production after initial fracturing to refracturing to production after refracturing—is systematically simulated. This method can be used not only for stress-fracture redirection simulation during shale gas refracturing, but also for numerical optimization of refracturing timing, well and layer selection, and design based on productivity. This improves the adaptability of shale gas refracturing processes, reduces field operation risks, and facilitates the improvement or restoration of shale gas well productivity and ultimate reservoir recovery.

[0015] As a further description of the present invention, the hydraulic fracture random expansion model includes: fracture flow equation, material balance equation, plane fracture stress equation, fracture expansion and turning criterion, hydraulic fracture and natural fracture intersection criterion and flow distribution criterion.

[0016] As a further description of the present invention, the method for simulating the random propagation of the initial hydraulic fracture is:

[0017] S1: Assign the initial hydraulic fracture length and net pressure of the fluid in the fracture based on the linear solution method;

[0018] S2: Update the crack tip unit, extend the crack length, and update the net pressure in the extended crack based on the flow equation;

[0019] S3: Substitute the net pressure of the fluid in the crack in S2 into the plane stress equation to obtain the crack width;

[0020] S4: Calculate the flow distribution in the crack according to the crack width obtained in S3 to obtain the crack mouth flow;

[0021] S5: Determine the convergence of the crack flow in S4 based on the material balance equation. If converged, execute S6; if not, return to S2 to change the crack tip extension length until the crack flow converges.

[0022] S6: Based on the fracture propagation and steering criteria, the fracture tip is redirected to detect whether the fracture tip intersects with a natural fracture and activates the natural fracture; if so, the flow is redistributed to the new fracture formed after the intersection, the net pressure value of the fluid in the new fracture is obtained, and the process returns to S2;

[0023] S7: Repeat S2 to S6 until the simulation time ends.

[0024] As a further description of the present invention, in said S6, the method for detecting whether the crack tip intersects with the natural crack is as follows: obtaining the turning direction of the crack tip, judging whether the crack tip is approaching the natural crack according to the turning direction of the crack tip; if the crack tip is approaching the natural crack, further judging whether the natural crack is at r=r c Is shear slip along the natural crack section? If the natural crack is at r = r c If shear slip occurs at , the crack tip intersects with the natural crack; where r represents the distance between the crack tip and the natural crack, r c It represents the critical radius when the induced tensile stress on the natural fracture surface reaches the tensile strength of the rock.

[0025] As a further description of the present invention, it is determined that the natural fracture is at r = r c The method to determine whether shear slip occurs along the cross section of a natural fracture is to compare the sum of the friction and cohesion on the surface of the natural fracture with the shear stress acting on the surface of the natural fracture. If the absolute value of the shear stress acting on the surface of the natural fracture is less than the sum of the friction and cohesion on the surface of the natural fracture, then shear slip will not occur in the natural fracture.

[0026] As a further description of the present invention, in S6, before redistributing the flow to the new fractures formed after the intersection, the equivalent conductivity between the fracture units is obtained through the flow continuity relationship.

[0027] As a further description of the present invention, the method for obtaining the reservoir production-induced stress is:

[0028] Establishing a shale multi-scale fluid-solid coupled horizontal well seepage model, wherein the shale multi-scale fluid-solid coupled horizontal well seepage model includes: a solid deformation control equation and a gas multi-scale seepage control equation;

[0029] According to the relationship between the loss of propped fracture conductivity and the effective closure stress, the solid deformation control equation and the gas multi-scale seepage control equation are numerically discretized using a fully implicit finite volume method, and the reservoir production-induced stress is obtained through coupled solution.

[0030] In another aspect, the present invention provides a shale reservoir refracturing stress-crack redirection simulation system, comprising:

[0031] The initial hydraulic fracture random expansion simulation unit is used to establish a hydraulic fracture random expansion model and initialize model parameters; and perform an initial hydraulic fracture random expansion simulation based on the hydraulic fracture random expansion model and the model parameters to obtain an initial fracture morphology;

[0032] a production fracture conductivity loss evaluation experimental unit, configured to conduct a production fracture conductivity loss evaluation experiment based on the initial fracture morphology, and obtain a relationship between the propped fracture width and the effective closure stress, and a relationship between the propped fracture conductivity loss and the effective closure stress;

[0033] a total stress field simulation unit before refracturing, configured to simulate the total stress field before refracturing based on the experimental results of the production fracture conductivity loss evaluation experimental unit, and linearly superimpose the obtained initial closed fracture deformation induced stress and reservoir production induced stress to form the total stress field before refracturing;

[0034] The re-fracturing crack extension simulation unit is used to perform re-fracturing crack extension simulation according to the hydraulic fracture random extension model in the total stress field before re-fracturing, and obtain the shale reservoir re-fracturing stress-crack redirection simulation result.

[0035] As a further description of the present invention, the primary hydraulic fracture random expansion simulation unit includes:

[0036] Hydraulic fracture random expansion model memory, used to store the hydraulic fracture random expansion model, including: fracture flow equation, material balance equation, plane fracture stress equation, fracture expansion and turning criteria, hydraulic fracture and natural fracture intersection criteria and flow distribution criteria;

[0037] Parameter memory, used to store initialized model parameters;

[0038] The hydraulic fracture random expansion model calculator is used to substitute the model parameters into the hydraulic fracture random expansion model calculation and output the initial fracture shape.

[0039] As a further description of the present invention, the total stress field simulation unit before refracturing includes:

[0040] A crack deformation induced stress calculator, configured to calculate the crack deformation induced stress based on the relationship between the support crack width and the effective closure stress;

[0041] A shale multi-scale fluid-solid coupled horizontal well seepage model storage device, used for storing the shale multi-scale fluid-solid coupled horizontal well seepage model including: solid deformation control equations and gas multi-scale seepage control equations;

[0042] The reservoir production-induced stress calculator is used to substitute the relationship between the propped fracture conductivity loss and the effective closure stress into the shale multi-scale fluid-solid coupled horizontal well seepage model to calculate the reservoir production-induced stress.

[0043] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0044] 1. The embodiments of the present invention provide a shale reservoir refracturing stress-crack redirection simulation method and system, which can simulate the entire process of "initial fracturing crack expansion - production after initial fracturing - refracturing crack expansion - production after refracturing" in shale reservoirs;

[0045] 2. A shale reservoir refracturing stress-crack redirection simulation method and system provided by the embodiments of the present invention can be used to analyze the shale gas refracturing process and reduce operational risks;

[0046] 3. The embodiment of the present invention provides a shale reservoir repeated fracturing stress-crack redirection simulation method and system, which is conducive to improving or restoring the productivity of shale gas wells and increasing the ultimate recovery rate of the reservoir. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without making any creative efforts.

[0048] Figure 1 The distribution map of natural fractures in the reservoir provided in Example 1 of the present invention;

[0049] Figure 2A schematic flow chart of a method for solving a hydraulic fracture random propagation model provided in Example 1 of the present invention;

[0050] Figure 3 A schematic diagram of the initial pressure fracture morphology of a reservoir provided in Example 1 of the present invention;

[0051] Figure 4 Schematic diagram of the short-term flow conductivity test results of 40 / 70 mesh quartz sand provided in Example 1 of the present invention;

[0052] Figure 5 This is a schematic diagram of the short-term conductivity test results of the 70 / 140 mesh proppant provided in Example 1 of the present invention;

[0053] FIG6( a ) is a schematic diagram of the horizontal stress difference of a reservoir after initial fracturing and one year of production, provided in Example 1 of the present invention;

[0054] FIG6( b ) is a schematic diagram of the horizontal stress difference of the reservoir after the initial fracturing of the reservoir provided in Example 1 of the present invention and after 3 years of production;

[0055] FIG6( c ) is a schematic diagram of the horizontal stress difference of the reservoir after the initial fracturing and production for 5 years provided in Example 1 of the present invention;

[0056] Figure 7 A schematic diagram of the fracture morphology of a reservoir after repeated fracturing provided in Example 1 of the present invention;

[0057] FIG8( a ) is a schematic diagram of pore pressure distribution without repeated fracturing provided in Example 1 of the present invention;

[0058] FIG8( b ) is a schematic diagram of pore pressure distribution after repeated fracturing for one year according to Example 1 of the present invention;

[0059] FIG8( c ) is a schematic diagram of pore pressure distribution after repeated fracturing for three years according to Example 1 of the present invention;

[0060] FIG8( d ) is a schematic diagram of pore pressure distribution after repeated fracturing for 5 years according to Example 1 of the present invention;

[0061] FIG9( a ) is a schematic diagram of the distribution of adsorbed gas content without repeated fracturing provided in Example 1 of the present invention;

[0062] FIG9( b ) is a schematic diagram of pore pressure distribution after repeated fracturing for one year according to Example 1 of the present invention;

[0063] Figure 9(c) is a schematic diagram of the pore pressure distribution after repeated fracturing for three years according to Example 1 of the present invention.

[0064] FIG9( d ) is a schematic diagram of pore pressure distribution after repeated fracturing for 5 years according to Example 1 of the present invention;

[0065] Figure 10 Schematic diagram of daily gas production of the reservoir after 1, 3, and 5 years of production without re-fracturing provided in Example 1 of the present invention;

[0066] Figure 11 Schematic diagram of the cumulative gas production of the reservoir after 1, 3 and 5 years of production without repeated fracturing provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0067] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples and drawings. The exemplary embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0068] Example 1

[0069] Since the existing refracturing technology for shale gas horizontal wells is still in the exploratory and experimental stage, the problems of stress field analysis before refracturing and new fracture redirection have not been well solved. As a result, the use of existing refracturing technology for shale gas horizontal wells in field construction faces engineering problems such as poor process adaptability and high operational risks. In addition, no significant progress has been made in restoring shale gas well production capacity and improving the ultimate recovery rate of the reservoir.

[0070] In response to the above technical problems, this embodiment provides a shale reservoir repeated fracturing stress-crack redirection simulation method. By establishing a hydraulic fracture random expansion and fracture deformation stress field model, the fracture deformation induced stress field simulation under complex fracture morphology and the hydraulic fracture random expansion simulation under non-uniform stress field conditions are realized. Further, based on the accurate description of the gas migration law in multi-scale shale gas reservoirs, a fluid-solid coupled horizontal well seepage model is further established. Based on linear elastic mechanics, fracture mechanics, seepage mechanics and experimental evaluation, the whole process of "initial fracturing fracture expansion-production after initial fracturing-re-fracturing fracture expansion-production after re-fracturing" of shale reservoirs is systematically simulated. Specifically, the following steps are included:

[0071] Step 1: Set up a shale reservoir refracturing stress-fracture redirection simulation scenario.

[0072] This example provides a typical shale reservoir with a flow area of 500m×500m×40m, within which there are randomly distributed Figure 1 For the random natural fractures shown, both the initial reservoir matrix pressure and the initial fracture pressure are 30 MPa.

[0073] In addition, in this embodiment, the horizontal section of the reservoir is divided into 6 segments and 14 clusters for fracturing. The specific segmentation and clustering design is detailed in Table 1.

[0074]

[0075] Table 1 Reservoir initial fracturing stage clustering design

[0076] Step 2: Initial hydraulic fracture random propagation simulation.

[0077] Step 2.1: Establish a random hydraulic fracture propagation model.

[0078] Since the initial stress field is an undisturbed in-situ stress field, in order to obtain the fracture morphology after the initial random expansion of the hydraulic fracture, it is necessary to describe the random expansion law of the hydraulic fracture. Therefore, this embodiment establishes a random expansion model of the hydraulic fracture and performs the initial random expansion simulation of the hydraulic fracture according to the random expansion model of the hydraulic fracture.

[0079] Furthermore, the hydraulic fracture random expansion model includes: fracture flow equation, material balance equation, plane fracture stress equation, fracture expansion and turning criterion, hydraulic fracture and natural fracture intersection criterion and flow distribution criterion.

[0080] in,

[0081] The flow equation in the crack is:

[0082]

[0083] Where q f Represents the volume flow rate of the crack cross section, in m 3 / s,h f Indicates the crack height, in m; w f Indicates the width of the hydraulic fracture, in m; μ f Indicates fluid viscosity, unit is Pa·s; p f represents the fluid pressure in the fracture, in Pa; E represents the Young's modulus of rock, in Pa; σ n It represents the normal stress acting on the fracture surface, and its unit is Pa; v represents the Poisson’s ratio of the reservoir rock, which is dimensionless.

[0084] The material balance equation includes the local material balance equation and the global material balance equation.

[0085] For tight shale reservoirs, ignoring the loss of fluid to the matrix, the injected fluid volume is equal to the dynamic volume of the hydraulic fracture, and the local fluid material balance equation is:

[0086] Global material balance equation:

[0087] In formula (4), QT(t) represents the total pumping displacement, in units of m 3 / s; Np represents the number of perforation clusters, which is dimensionless, assuming that one perforation cluster extends one fracture; L(t) represents the total length of the hydraulic fracture in time t, in meters; Indicates the average crack width in m.

[0088] In shale reservoirs with well-developed natural fractures, where hydraulic fractures intersect with natural fractures and multiple hydraulic fractures extend simultaneously, the width of each hydraulic fracture unit is affected by stress interference. It is necessary to establish a plane fracture stress equation to obtain the dynamic width of each fracture unit and couple it with the flow equation within the fracture to solve it.

[0089] Based on the modified two-dimensional displacement discontinuity method, it is assumed that there are normal and tangential constant displacement discontinuities on each fracture element, and the elastic body remains unchanged under the influence of the displacement discontinuity. The net fluid pressure is the boundary condition of the hydraulic fracture deformation stress field model, and the displacement discontinuity of each fracture element j is and The calculation formula for the tangential and normal stresses generated at the midpoint of crack element i is:

[0090] The height correction factor is expressed as G ij :

[0091] In formulas (5) and (6), Represents the displacement discontinuity of each crack element j and The tangential stress generated at the midpoint of the crack element i, N represents the number of discrete element cracks; Represents the displacement discontinuity of each crack element j and Normal stress generated at the midpoint of crack element i; G ij represents the altitude correction factor; and are all boundary stress influence coefficients, among which, Represents the unit tangential displacement discontinuity value of crack element j The corresponding shear stress at the midpoint of crack element i is, Represents the unit tangential displacement discontinuity value of crack element j The normal stress at the midpoint of the corresponding crack element i is, and The unit is Pa·m -1 ; Indicates the unit normal displacement discontinuity value with respect to element j The corresponding shear stress at the midpoint of crack element i is, Indicates the unit normal displacement discontinuity value with respect to element j The normal stress at the midpoint of the corresponding crack element i is, and The unit is Pa·m -1 ;d ij Represents the distance between crack unit i and crack unit j, in m; α f and β f Are all empirical constants, take α f =1,β f =2.3.

[0092] Equation (5) consists of 2N algebraic equations, which is the same as the number of unknowns. By finding all the boundary stress influence coefficients in the equation and solving the equation system, the displacement discontinuity of each crack unit can be obtained, where the normal displacement discontinuity of each crack unit is equivalent to its dynamic crack width.

[0093] In the actual fracturing process, it is generally believed that hydraulic fracture expansion is mainly in the three modes of opening type (type I), shear type (type II) and tearing type (type III). The maximum circumferential tensile stress intensity factor theory is used as the criterion for composite fracture expansion. The stress field distribution at the fracture tip is:

[0094] According to the maximum circumferential stress theory, the crack tip should extend in the direction where the circumferential stress reaches its maximum, that is, the following conditions must be met: K I sinθ+K II (3cosθ-1)=0(8);

[0095] The first and second stress intensity factors K of the crack tip element I , K II Determined by the shear displacement discontinuity and normal displacement discontinuity at the crack tip:

[0096] In formulas (7) to (9), σ r Indicates the radial stress at the crack tip, in Pa; σ θ represents the circumferential stress at the crack tip, in Pa; τ rθ represents the tangential stress at the crack tip, in Pa; r and θ represent the polar coordinates of the point near the crack tip, in m; K I Represents the first type of stress intensity factor, unit is Pa·m 1 / 2 ;K II Represents the second type of stress intensity factor, unit is Pa·m 1 / 2; Dn represents the normal displacement discontinuity at the crack tip, with the unit of m; Ds represents the shear displacement discontinuity at the crack tip, with the unit of m; G represents the shear modulus of the rock, with the unit of Pa; ν represents the Poisson's ratio of the reservoir rock, which is dimensionless; a represents half of the unit length of the crack tip, with the unit of m.

[0097] During the extension of hydraulic fractures in shale reservoirs, tensile failure and shear failure will occur simultaneously. Therefore, it is necessary to analyze the changes in the stress field when considering the intersection of hydraulic fractures and natural fractures. When the hydraulic fracture approaches the natural fracture, the stress distribution at the hydraulic fracture tip is:

[0098] in,

[0099]

[0100] In formulas (10) to (13), r and θ represent the polar coordinates of the crack endpoints, in meters; σ H Represents the maximum horizontal principal stress, in Pa; σ h Indicates the minimum horizontal principal stress, in Pa; K I represents the first kind of stress intensity factor, K II represents the second type of stress intensity factor, K I and K II The unit is Pa·m 1 / 2 ; r c It represents the critical radius when the induced tensile stress on the natural fracture surface reaches the tensile strength of the rock, in m; T0 represents the tensile strength of shale, in Pa.

[0101] Based on the stress distribution at the hydraulic fracture tip, it is necessary to determine whether the natural fracture is at r = r c The shear slip along the natural fracture section is used to determine whether the hydraulic fracture is captured and does not extend along another natural fracture surface. If the natural fracture is at r = r c If shear slip does not occur, the hydraulic fracture will directly pass through the natural fracture. When the sum of the friction force and cohesion acting on the surface of the natural fracture is greater than the shear stress acting on the fracture surface, the natural fracture will not undergo shear slip.

[0102] That is: |τ β |<S0+μ0σ nβ (14);

[0103]

[0104]

[0105] In formulas (14) to (16), μ0 represents the friction coefficient of the natural crack surface, dimensionless; S0 represents the cohesion of the natural crack, unit is Pa; τ β represents the shear stress acting on the natural crack surface, σ nβ represents the shear stress and normal stress acting on the surface of the natural crack, τ β and σ nβ The unit is Pa.

[0106] Whenever the hydraulic fracture tip unit is updated, check whether the fracture tip intersects with the natural fracture. If the hydraulic fracture intersects the natural fracture, use equations (15) and (16) to calculate the stress at the critical point of the fracture tip. This stress is then transformed into the plane of the intersecting natural fracture, and the slip of the natural fracture is predicted using the Mohr-Coulomb criterion. When shear failure occurs in the natural fracture, the hydraulic fracture is considered to be captured by the natural fracture, and the intersecting natural fracture becomes a displacement discontinuous unit.

[0107] When a hydraulic fracture is captured by a natural fracture, the tip of the hydraulic fracture must be artificially moved to the end point of the activated natural fracture. Due to the different apertures of the fracture units, when calculating the flow flux between fracture units, it is necessary to derive the equivalent conductivity between the units using the flow continuity relationship. The flow between fracture unit i and fracture unit j is:

[0108]

[0109] When a hydraulic fracture intersects a natural fracture, the three fracture units are connected. The delta-star transformation based on resistivity calculation can be used to equivalently calculate the conductivity between the fracture units, that is:

[0110]

[0111] in,

[0112] q ij represents the flow rate between fracture unit i and fracture unit j when the hydraulic fracture is captured by the natural fracture, T ij It represents the conductivity between fracture unit i and fracture unit j when the hydraulic fracture intersects the natural fracture, T ik It represents the conductivity between fracture unit i and fracture unit k when the hydraulic fracture intersects the natural fracture, T jk represents the conductivity between fracture unit j and fracture unit k when the hydraulic fracture intersects the natural fracture;

[0113] In formulas (17) to (23), μ f represents the viscosity of the fluid in the fracture, in Pa·s; p f Indicates the crack unit pressure, in Pa; A fThe cross-sectional area of the fracture unit is expressed in m; D represents the distance from the center point of the fracture unit to the intersection point, in m; k f Indicates the fracture unit permeability, in m 2 .

[0114] The boundary conditions used to solve the random propagation model of hydraulic fractures need to indicate the flow state at both ends of the fracture. At the entrance of the fracture, the flow rate is equal to the injection rate, while at the tip of the fracture, the net pressure is 0, that is:

[0115] q f (0,t)=q0(t);t>0(24);

[0116] p f (L f ,t)=0;t>0(25);

[0117] In the initial state, that is, at time t=0, the length and pressure of the crack are both 0, that is:

[0118] L f (0)=0,p f (0,0)=0(26);

[0119] In formulas (24) to (26), q f (0,t) represents the flow velocity of the fluid at the fracture entrance, q0(t) represents the rate at which the fluid is injected into the fracture entrance, and p f (L f ,t) represents the net pressure of the fluid at the crack tip, L f (0) represents the length of the crack in the initial state, p f (0,0) represents the pressure of the crack in the initial state.

[0120] Step 2.2: Initialize the parameters of the hydraulic fracture random propagation model.

[0121] The detailed geological and engineering parameters of the model input are shown in Table 2:

[0122]

[0123] Table 2 Geological and engineering parameters

[0124] Step 2.3: Substitute the hydraulic fracture random propagation model parameters initialized in step 2.2 into the hydraulic fracture random propagation model established in step 2.1 and solve the model according to the following steps:

[0125] S1: Assign the initial hydraulic fracture length and net pressure of the fluid in the fracture based on the linear solution method;

[0126] S2: Update the crack tip unit, extend the crack length, and update the net pressure in the extended crack based on the flow equation;

[0127] S3: Substitute the net pressure of the fluid in the crack in S2 into the plane stress equation to obtain the crack width;

[0128] S4: Calculate the flow distribution in the crack according to the crack width obtained in S3 to obtain the crack mouth flow;

[0129] S5: Determine the convergence of the crack flow in S4 based on the material balance equation. If converged, execute S6; if not, return to S2 to change the crack tip extension length until the crack flow converges.

[0130] S6: Based on the fracture propagation and steering criteria, the fracture tip is redirected to detect whether the fracture tip intersects with a natural fracture and activates the natural fracture; if so, the flow is redistributed to the new fracture formed after the intersection, the net pressure value of the fluid in the new fracture is obtained, and the process returns to S2;

[0131] S7: Repeat S2 to S6 until the simulation time ends.

[0132] The method flow for solving the hydraulic fracture random expansion model can be referred to Figure 2 .

[0133] After solving the model, the initial pressure fracture morphology of the reservoir is obtained as follows: Figure 3 shown.

[0134] Step 3: Conduct an experiment to evaluate the loss of conductivity of production fractures after fracturing.

[0135] Conducting experiments to evaluate the loss of conductivity in post-fracture production fractures reveals the relationship between propped fracture width and effective closure stress, which is used to calculate deformation-induced stress in initially closed fractures. Furthermore, the relationship between propped fracture conductivity loss and effective closure stress is used to calculate production-induced stress. By varying the closure stress acting on the rock slab, experimental results under different closure stress conditions can be obtained, serving as important input parameters for stress simulations in shale reservoirs prior to refracturing.

[0136] According to API standards, shale outcrops were processed into slabs with semicircular ends. During the experiment, two standard shale slabs were placed at the upper and lower positions of the diversion chamber, and proppant was placed between the slabs. The proppant used was 70 / 140 mesh and 40 / 70 mesh quartz sand, with an apparent density of 1.33-1.44 g / cm 3 The proppant used in the experiment can be selected according to the specific conditions of the mine construction application. Considering the uneven placement of proppant in hydraulic fractures and sand paving in branch seams, the experimental setting is: 0.5kg / m 2 , 1.0kg / m2 , 1.5kg / m 2 , 2.0kg / m 2 , 2.5kg / m 2 and 3.0kg / m 2 The concentration of sand was adjusted and the closing stress on the crack surface was gradually increased from 10 MPa to 65 MPa. The specific experimental plan is shown in Table 3.

[0137]

[0138] Table 3 Experimental scheme for evaluating the short-term conductivity loss of production fractures

[0139] Figure 4 and Figure 5 These are the experimental test results of short-term conductivity of artificial fractures under conditions of different quartz sand particle sizes and sand concentrations.

[0140] Step 4: Based on the experimental results obtained in step 3, simulate the total stress field before repeated fracturing.

[0141] Based on the theory of linear elasticity, the stress field of the reservoir before refracturing is the linear superposition of the deformation-induced stress of the initial closed fracture and the production-induced stress.

[0142] Step 4.1: Based on the plane crack stress equation established in Step 2, first calculate the crack deformation-induced stress. For a pressure-bearing crack in a uniform isotropic elastic body, the final stress component of this problem is the stress component value caused by the constant displacement discontinuity at the crack boundary. Based on the principles of linear elasticity, the stress component at any point in the global coordinate system, that is, the induced deformation stress of the crack, is calculated as:

[0143]

[0144] in,

[0145]

[0146] In formulas (27) to (33): and represents the constant displacement discontinuity on each crack element, and β represents the local coordinate system of the crack element. The angle between the axis and the x-axis of the global coordinate system; a represents the half-length of the crack unit, in meters.

[0147] Step 4.2: Establish a horizontal well flow model for shale multiscale fluid-solid coupling to calculate production-induced stress. The model includes the governing equations for solid deformation and multiscale gas flow.

[0148] The governing equation for solid deformation is:

[0149] in,

[0150]

[0151] In formulas (34) to (38), G represents the shear modulus, in Pa; λ represents the first Lame constant, in Pa; ε v represents volumetric strain, which is dimensionless; ε s represents the desorption-induced volume strain, which is dimensionless; ε L represents the maximum desorption volume strain, which is dimensionless; p L Indicates Langmuir pressure, unit is Pa; p m represents the matrix pressure, in Pa; u represents the displacement vector, in m; E represents the Young's modulus, in Pa; ν represents the Poisson's ratio, which is dimensionless.

[0152] The governing equation for gas flow in the shale matrix system is:

[0153]

[0154] q μ =(1-φ m )M g c μ (41);

[0155] In formulas (39) to (41): gm Indicates the density of the gas in the matrix system, in kg / m 3 ;μ gm Indicates the viscosity of the gas in the matrix system, in Pa·s; k appm It represents the apparent permeability of gas in the matrix system, in m 2 ;φ m represents the effective porosity in the matrix system and is dimensionless; q μ Indicates the amount of adsorbed gas per unit shale volume, in kg / m 3 ;W mf represents the mass flow exchange term between the matrix system and the fracture system, with the unit being kg / s; p m It represents the pore pressure of the matrix system, in Pa.

[0156] The governing equation for gas flow in a shale fracture system is:

[0157]

[0158] The source and sink of the production well are set in the fracture unit, and its production term is:

[0159]

[0160] In formulas (42) to (44): qwell Indicates the output item, the unit is kg / s; p f Indicates the pressure inside the hydraulic fracture unit, in Pa; p wf Indicates the bottom hole pressure, the unit is Pa; ρ gf Indicates the density of gas in the fracture system, in kg / m 3 ;μ gf represents the viscosity of the gas in the matrix system, in Pa·s; w f Indicates the width of the crack unit, in m; k f Indicates the fracture unit permeability, in m 2 ; r e Indicates the equivalent radius of the wellbore, in m; r w Indicates the wellbore radius, in m; d xf Indicates the length of the crack unit, in m; h f Represents the fracture unit height (reservoir thickness), in meters.

[0161] For the establishment of a horizontal well seepage model for multi-scale fluid-solid coupling in shale, under initial conditions, it is assumed that the pressure at each point in the fracture system and matrix system is the original formation pressure, that is: p m (x,y,t)| t＝0 =p f (x,y,t)| t＝0 =p0 (46);

[0162] The outer boundary of the model is closed, so the outer boundary condition is:

[0163] If the inner boundary adopts constant bottom hole pressure production, the inner boundary condition is:

[0164] In order to establish a horizontal well seepage model with multi-scale fluid-solid coupling in shale, the fully implicit volume method is used to numerically discretize the solid deformation control equation and the gas multi-scale seepage control equation, and the reservoir production-induced stress is obtained through coupled solution.

[0165] In the actual calculation process, the initial dynamic width of the hydraulic fracture and the maximum sand filling concentration at the fracture opening are first obtained. Under the condition of the initial effective closure pressure, the closure width of each fracture unit can be obtained through the equivalent principle. Based on the experimental results of the production fracture conductivity evaluation in step 2 and a production pressure difference of 5 MPa, considering the effective stress acting on the fracture surface as 45 MPa, the corresponding fracture unit width and conductivity are substituted into the horizontal well seepage model of shale multi-scale fluid-solid coupling to obtain the production-induced stress of the initial hydraulic fracture. Further linear superposition of the induced stress field of the initial hydraulic fracture deformation can be obtained to obtain the total stress field distribution of the shale reservoir before repeated fracturing. For a typical embodiment, the total stress field distribution of the reservoir at different production times after the initial fracturing is shown in Figure 6. Figure 6(a) is a schematic diagram of the horizontal stress difference of the reservoir after one year of production after the initial fracturing, Figure 6(b) is a schematic diagram of the horizontal stress difference of the reservoir after three years of production after the initial fracturing, and Figure 6(c) is a schematic diagram of the horizontal stress difference of the reservoir after five years of production after the initial fracturing.

[0166] Step 5: In the total stress field before refracturing, perform refracturing crack propagation simulation according to the hydraulic fracture random propagation model.

[0167] In view of the analysis of the simulation results of the stress field before repeated fracturing, the re-perforation fracturing method is used to simulate the fracture expansion and post-fracturing production dynamics, and it is assumed that the middle part of the adjacent fractures of the initial fracturing is perforated and fractured. The stress field before repeated fracturing is the total stress field established in step 4, and its value is the linear superposition of the initial closed fracture deformation induced stress and the production induced stress. The repeated fracturing fracture expansion simulation is performed with reference to the hydraulic fracture random expansion model established in step 2. It can be seen from the total stress field distribution of the reservoir after 1 year, 3 years and 5 years of production after the initial fracturing in step 4 that the stress disturbance caused by production on both sides of the fracture is very limited. Therefore, repeated fracturing after 1 year, 3 years and 5 years of production has almost no effect on the fracture morphology, such as Figure 7 shown.

[0168] Next, combined with productivity simulation, the above stress-fracture redirection results of shale reservoir refracturing were applied to the optimization of refracturing time nodes.

[0169] Figure 8 shows the reservoir pore pressure distribution for refracturing at 1, 3, and 5 years of production, and for a total of 10 years of production without refracturing. The simulation results show that refracturing increases the spacing between fractures, increasing the fracture conductivity area and complexity, thereby achieving a larger seepage control range. On the other hand, the earlier the refracturing, the greater the decrease in reservoir pore pressure. This difference is not obvious from the pore pressure distribution, but it is indirectly reflected in the distribution of reservoir adsorbed gas content, as shown in Figure 9. Figure 9(a) shows the adsorbed gas content distribution without refracturing, Figure 9(b) shows the pore pressure distribution after 1 year of production with refracturing, Figure 9(c) shows the pore pressure distribution after 3 years of production with refracturing, and Figure 9(d) shows the pore pressure distribution after 5 years of production with refracturing.

[0170] Figure 10 、 Figure 11 Figure 2 shows the daily and cumulative gas production curves for a 10-year refracturing reservoir at different time points. The simulation results show that refracturing can improve reservoir recovery, and the earlier the refracturing is performed, the greater the increase in reservoir recovery. Therefore, for reservoirs with large initial fracture spacing and horizontal stress differences, reperforation can be used earlier for secondary refracturing and production enhancement.

[0171] Example 2

[0172] This embodiment provides a system corresponding to the shale reservoir refracturing stress-crack redirection simulation method described in Example 1, including:

[0173] The initial hydraulic fracture random expansion simulation unit is used to establish a hydraulic fracture random expansion model and initialize model parameters; and perform an initial hydraulic fracture random expansion simulation based on the hydraulic fracture random expansion model and the model parameters to obtain an initial fracture morphology;

[0174] a production fracture conductivity loss evaluation experimental unit, configured to conduct a production fracture conductivity loss evaluation experiment based on the initial fracture morphology, and obtain a relationship between the propped fracture width and the effective closure stress, and a relationship between the propped fracture conductivity loss and the effective closure stress;

[0175] a total stress field simulation unit before refracturing, configured to simulate the total stress field before refracturing based on the experimental results of the production fracture conductivity loss evaluation experimental unit, and linearly superimpose the obtained initial closed fracture deformation induced stress and reservoir production induced stress to form the total stress field before refracturing;

[0176] The re-fracturing crack extension simulation unit is used to perform re-fracturing crack extension simulation according to the hydraulic fracture random extension model in the total stress field before re-fracturing, and obtain the shale reservoir re-fracturing stress-crack redirection simulation result.

[0177] in,

[0178] The simulation unit for random propagation of initial hydraulic fractures includes:

[0179] Hydraulic fracture random expansion model memory, used to store the hydraulic fracture random expansion model, including: fracture flow equation, material balance equation, plane fracture stress equation, fracture expansion and turning criteria, hydraulic fracture and natural fracture intersection criteria and flow distribution criteria;

[0180] Parameter memory, used to store initialized model parameters;

[0181] The hydraulic fracture random expansion model calculator is used to substitute the model parameters into the hydraulic fracture random expansion model calculation and output the initial fracture shape.

[0182] Furthermore, the total stress field simulation unit before refracturing includes:

[0183] A crack deformation induced stress calculator, configured to calculate the crack deformation induced stress based on the relationship between the support crack width and the effective closure stress;

[0184] A shale multi-scale fluid-solid coupled horizontal well seepage model memory, used to store the shale multi-scale fluid-solid coupled horizontal well seepage model, wherein the shale multi-scale fluid-solid coupled horizontal well seepage model includes: solid deformation control equations and gas multi-scale seepage control equations;

[0185] The reservoir production-induced stress calculator is used to substitute the relationship between the propped fracture conductivity loss and the effective closure stress into the shale multi-scale fluid-solid coupled horizontal well seepage model to calculate the reservoir production-induced stress.

[0186] The specific implementation methods 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 implementation method 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 shale reservoir repeated fracturing stress-crack redirection simulation method, characterized in that: The following steps are involved: Establishing a hydraulic fracture random propagation model and initializing model parameters; performing an initial hydraulic fracture random propagation simulation based on the hydraulic fracture random propagation model and the model parameters to obtain an initial fracture morphology; The stochastic hydraulic fracture propagation model includes the following: the flow equation within the fracture, the material balance equation, the plane fracture stress equation, the fracture propagation and turning criterion, the intersection criterion between hydraulic fractures and natural fractures, and the flow distribution criterion. The flow equation within the fracture is specifically: Among them, q f represents the volume flow rate of the crack cross section, h f Indicates the crack height; w f Indicates the width of hydraulic fracture; μ f represents the fluid viscosity; p f represents the fluid pressure in the fracture; E represents the Young's modulus of rock; σ n represents the normal stress acting on the crack surface; the material balance equation includes the local material balance equation and the global material balance equation. The local material balance equation is specifically: The global material balance equation is specifically: Among them, Q T (t) represents the total pumping displacement; N p represents the number of perforation clusters; L(t) represents the total length of hydraulic fracture at time t; represents the average crack width; the plane crack stress equation is specifically: in, Represents the displacement discontinuity of each crack element j and The tangential stress generated at the midpoint of the crack element i, j = 1, 2, ... N; N is the number of discrete element cracks; Represents the displacement discontinuity of each crack element j and Normal stress generated at the midpoint of crack element i; G ij represents the altitude correction factor; and are boundary stress influence coefficients; d ij represents the distance between crack unit i and crack unit j; α f and β f are all empirical constants; the specific crack extension and turning criteria are: K I sinθ+K II (3cosθ-1)=0, where K I , K II denote the first and second type stress intensity factors of the crack tip unit respectively; θ denotes the polar coordinates of the point near the crack tip; the intersection criterion between hydraulic fractures and natural fractures is: |τ β |<S0+μ0σ nβ , where τ β represents the shear stress acting on the surface of the natural crack; S0 represents the cohesion of the natural crack; μ0 represents the friction coefficient of the natural crack surface; σ nβ represents the normal stress acting on the surface of the natural fracture; the flow distribution criterion is: Among them, q ij represents the flow rate between fracture unit i and fracture unit j when the hydraulic fracture is captured by the natural fracture; T ij represents the conductivity between fracture unit i and fracture unit j when the hydraulic fracture intersects the natural fracture; μf represents the viscosity of the fluid in the fracture; p fi represents the fracture unit pressure of fracture unit i; p fj represents the fracture element pressure of fracture element j; Conducting a production fracture conductivity loss evaluation experiment based on the initial fracture morphology to obtain experimental results, wherein the experimental results include: a relationship between the propped fracture width and the effective closure stress, and a relationship between the propped fracture conductivity loss and the effective closure stress; Performing a total stress field simulation before refracturing based on the experimental results to obtain initial closed fracture deformation induced stress and reservoir production induced stress; linearly superimposing the initial closed fracture deformation induced stress and the reservoir production induced stress to obtain the total stress field before refracturing; In the total stress field before refracturing, refracturing fracture propagation simulation is performed according to the hydraulic fracture random propagation model to obtain shale reservoir refracturing stress-crack redirection simulation results.

2. A shale reservoir repeated fracturing stress-crack redirection simulation method according to claim 1, characterized in that: The method for simulating the random propagation of the initial hydraulic fracture is: S1: Assign the initial hydraulic fracture length and net pressure of the fluid in the fracture based on the linear solution method; S2: Update the crack tip unit, extend the crack length, and update the net pressure in the extended crack based on the flow equation; S3: Substitute the net pressure of the fluid in the crack in S2 into the plane stress equation to obtain the crack width; S4: Calculate the flow distribution in the crack according to the crack width obtained in S3 to obtain the crack mouth flow; S5: Determine the convergence of the crack flow in S4 based on the material balance equation. If converged, execute S6; if not, return to S2 and change the crack tip extension length until the crack flow converges. S6: Based on the fracture propagation and steering criteria, the fracture tip is redirected to detect whether the fracture tip intersects with a natural fracture and activates the natural fracture; if so, the flow is redistributed to the new fracture formed after the intersection, the net pressure value of the fluid in the new fracture is obtained, and the process returns to S2; S7: Repeat S2 to S6 until the simulation time ends.

3. The method for simulating stress-crack redirection during repeated fracturing of a shale reservoir according to claim 2, characterized in that: In the above S6, the method for detecting whether the crack tip intersects with the natural crack is as follows: obtaining the turning direction of the crack tip, judging whether the crack tip is approaching the natural crack according to the turning direction of the crack tip; if the crack tip is approaching the natural crack, further judging whether the natural crack is at r=r c Is shear slip along the natural crack section? If the natural crack is at r = r c If shear slip occurs at , the crack tip intersects with the natural crack; where r represents the distance between the crack tip and the natural crack, r c It represents the critical radius when the induced tensile stress on the natural fracture surface reaches the tensile strength of the rock.

4. A shale reservoir repeated fracturing stress-crack redirection simulation method according to claim 3, characterized in that: Determine the natural fracture at r = r c The method to determine whether shear slip occurs along the cross section of a natural fracture is to compare the sum of the friction and cohesion on the surface of the natural fracture with the shear stress acting on the surface of the natural fracture. If the absolute value of the shear stress acting on the surface of the natural fracture is less than the sum of the friction and cohesion on the surface of the natural fracture, then shear slip will not occur in the natural fracture.

5. The method for simulating stress-crack redirection during repeated fracturing of a shale reservoir according to claim 2, characterized in that: In S6, before redistributing the flow rate to the new fractures formed after the intersection, the equivalent conductivity between the fracture units is obtained through the flow continuity relationship.

6. The method for simulating stress-crack redirection during repeated fracturing of a shale reservoir according to claim 1, characterized in that: The method for obtaining the reservoir production induced stress is: Establishing a shale multi-scale fluid-solid coupled horizontal well seepage model, wherein the shale multi-scale fluid-solid coupled horizontal well seepage model includes: a solid deformation control equation and a gas multi-scale seepage control equation; The solid deformation control equation and the gas multi-scale seepage control equation are numerically discretized using a fully implicit finite volume method. The relationship between the propped fracture conductivity loss and the effective closure stress is substituted into the equation, and the reservoir production-induced stress is obtained through coupled solution.

7. A shale reservoir repeated fracturing stress-crack redirection simulation system, characterized in that: include: The initial hydraulic fracture random expansion simulation unit is used to establish the hydraulic fracture random expansion model and initialize the model parameters; and performing an initial hydraulic fracture random expansion simulation based on the hydraulic fracture random expansion model and the model parameters to obtain an initial fracture morphology; The stochastic hydraulic fracture propagation model includes the following: the flow equation within the fracture, the material balance equation, the plane fracture stress equation, the fracture propagation and turning criterion, the intersection criterion between hydraulic fractures and natural fractures, and the flow distribution criterion. The flow equation within the fracture is specifically: Among them, q f represents the volume flow rate of the crack cross section, h f Indicates the crack height; w f Indicates the width of hydraulic fracture; μ f represents the fluid viscosity; p f represents the fluid pressure in the fracture; E represents the Young's modulus of rock; σ n represents the normal stress acting on the crack surface; the material balance equation includes the local material balance equation and the global material balance equation. The local material balance equation is specifically: The global material balance equation is specifically: Among them, Q T (t) represents the total pumping displacement; N p represents the number of perforation clusters; L(t) represents the total length of hydraulic fracture at time t; represents the average crack width; the plane crack stress equation is specifically: in, Represents the displacement discontinuity of each crack element j and The tangential stress generated at the midpoint of the crack element i, j = 1, 2, ... N; N is the number of discrete element cracks; Represents the displacement discontinuity of each crack element j and Normal stress generated at the midpoint of crack element i; G ij represents the altitude correction factor; and are boundary stress influence coefficients; d ij represents the distance between crack unit i and crack unit j; α f and β f are all empirical constants; the specific crack extension and turning criteria are: K I sinθ+K II (3cosθ-1)=0, where K I , K II denote the first and second type stress intensity factors of the crack tip unit respectively; θ denotes the polar coordinates of the point near the crack tip; the intersection criterion between hydraulic fractures and natural fractures is: |τ β |<S0+μ0σ nβ , where τ β represents the shear stress acting on the surface of the natural crack; S0 represents the cohesion of the natural crack; μ0 represents the friction coefficient of the natural crack surface; σ nβ represents the normal stress acting on the surface of the natural fracture; the flow distribution criterion is: Among them, q ij represents the flow rate between fracture unit i and fracture unit j when the hydraulic fracture is captured by the natural fracture; T ij represents the conductivity between fracture unit i and fracture unit j when the hydraulic fracture intersects the natural fracture; μ f represents the viscosity of the fluid in the crack; p fi represents the fracture unit pressure of fracture unit i; p fj represents the fracture element pressure of fracture element j; a production fracture conductivity loss evaluation experimental unit, configured to conduct a production fracture conductivity loss evaluation experiment based on the initial fracture morphology, and obtain the relationship between the propped fracture width and the effective closure stress, and the relationship between the propped fracture conductivity loss and the effective closure stress; a total stress field simulation unit before refracturing, configured to simulate the total stress field before refracturing based on the experimental results of the production fracture conductivity loss evaluation experimental unit, and linearly superimpose the obtained initial closed fracture deformation induced stress and reservoir production induced stress to form the total stress field before refracturing; The re-fracturing crack extension simulation unit is used to perform re-fracturing crack extension simulation according to the hydraulic fracture random extension model in the total stress field before re-fracturing, and obtain the shale reservoir re-fracturing stress-crack redirection simulation result.

8. The shale reservoir repeated fracturing stress-crack redirection simulation system according to claim 7, characterized in that: The initial hydraulic fracture random expansion simulation unit includes: Hydraulic fracture random expansion model memory, used to store the hydraulic fracture random expansion model, including: fracture flow equation, material balance equation, plane fracture stress equation, fracture expansion and turning criteria, hydraulic fracture and natural fracture intersection criteria and flow distribution criteria; Parameter memory, used to store initialized model parameters; The hydraulic fracture random expansion model calculator is used to substitute the model parameters into the hydraulic fracture random expansion model calculation and output the initial fracture shape.

9. A shale reservoir repeated fracturing stress-crack redirection simulation system according to claim 7 or 8, characterized in that: The total stress field simulation unit before refracturing includes: A crack deformation induced stress calculator, used to calculate the crack deformation induced stress based on the relationship between the support crack width and the effective closure stress; A shale multi-scale fluid-solid coupled horizontal well seepage model memory, used to store the shale multi-scale fluid-solid coupled horizontal well seepage model, wherein the shale multi-scale fluid-solid coupled horizontal well seepage model includes: solid deformation control equations and gas multi-scale seepage control equations; The reservoir production-induced stress calculator is used to substitute the relationship between the propped fracture conductivity loss and the effective closure stress into the shale multi-scale fluid-solid coupled horizontal well seepage model to calculate the reservoir production-induced stress.

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